As moscafj's answer correctly states, the lowest average temp on that grill is more like 180-200F so you annihilated that poor bird! Even though the final temp may have been 150, it was almost certainly much hotter than that at some point (if the internal meat was firm and white this is certainly the case). But also, the idea of "low and slow" for BBQing is because your typical BBQ meats, like pork shoulder and beef brisket have tons of connective tissue which breaks down over time, along with tons of fat which keeps things moist throughout the cook (because it slowly gelatinizes into deliciousness). Skinless breast has none of that and is notoriously hard to keep moist regardless of how you cook it.

So really unless you know what you are doing it's a horrible cut of meat to smoke -- and it certainly should never be smoked for that long regardless. Whole chickens should be checked after an hour with an average smoke temp of 200 and will probably be done by 1.5-2 hours.

Additionally, apple wood is not a super strong flavor to begin with, but it's also important to keep in mind that smoke adheres and penetrates the meat best when it's cold and stops "sticking" to the meat once the outer layer gets fairly warm (and pretty much stops doing anything good after 130-140). Given the grill temp you would have hit that fairly quickly and thus the smoke really was only flavoring the meat for ~30 mins. This is why when you are smoking something like pulled pork you are only trying to get the good 'blue' smoke for the initial hours of the cook and after that it's much more about applying low and slow heat to bring the internal meat to temp -- you really don't want to be smoking it the whole time. In fact, it's often bad to do so because smoking can quickly go from adding a nice flavor to adding a lot of bitterness and unwanted flavors if you overdo it.

So TLDR, wrong cut, wrong amount of time, and wrong temp.

As moscafj's answer correctly states, the lowest average temp on that grill is more like 180-200F so you annihilated that poor bird! Even though the final temp may have been 150, it was almost certainly much hotter than that at some point (if the internal meat was firm and white this is certainly the case). But also, the idea of "low and slow" for BBQing is because your typical BBQ meats, like pork shoulder and beef brisket have tons of connective tissue which breaks down over time, along with tons of fat which keeps things moist throughout the cook (because it slowly gelatinizes into deliciousness). Skinless breast has none of that and is notoriously hard to keep moist regardless of how you cook it.

So really unless you know what you are doing it's a horrible cut of meat to smoke -- and it certainly should never be smoked for that long regardless. Whole chickens should be checked after an hour with an average smoke temp of 200 and will probably be done by 1.5-2 hours. In practice, since opening smokers is undesirable (you lose a lot of heat), you should have an oven-safe type thermometer so you always know what temperature the meat is. Ideally, have one with multiple inputs so you can monitor multiple zones in the meat and/or also monitor the temp of the air in the grill.

Additionally, apple wood is not a super strong flavor to begin with, but it's also important to keep in mind that smoke adheres and penetrates the meat best when it's cold and stops "sticking" to the meat once the outer layer gets fairly warm (and pretty much stops doing anything good after 130-140). Given the grill temp you would have hit that fairly quickly and thus the smoke really was only flavoring the meat for ~30 mins. This is why when you are smoking something like pulled pork you are only trying to get the good 'blue' smoke for the initial hours of the cook and after that it's much more about applying low and slow heat to bring the internal meat to temp -- you really don't want to be smoking it the whole time. In fact, it's often bad to do so because smoking can quickly go from adding a nice flavor to adding a lot of bitterness and unwanted flavors if you overdo it.

So TLDR, wrong cut, wrong amount of time, and wrong temp.

As moscafj's answer correctly states, the lowest average temp on that grill is more like 180-200F so you annihilated that poor bird! Even though the final temp may have been 150, it was almost certainly much hotter than that at some point (if the internal meat was firm and white at the end this is certainly the case). But also, the idea of "low and slow" for bbq is because your typical bbq meats, like pork shoulder and beef brisket has tons of connective tissue which breaks down over time, along with tons of fat which keeps things moist throughout the cook (because it slowly gelatinizes into deliciousness). Skinless breast has none of that and is notoriously hard to keep moist in general.

So really unless you know what you are doing it's a horrible cut of meat to smoke -- and it certainly should never be smoked for that long regardless. Whole chickens should be checked after an hour with an average smoke temp of 200 and will probably be done by 1.5-2 hours.

Additionally, apple wood is not a super strong flavor to begin with but it's also important to keep in mind that smoke stops "sticking" to the meat once you get above ~140F. You probably hit that fairly quickly given the cut and grill temp. This is why when you are doing something like pulled pork on a smoker like that you are only trying to get the good 'blue' smoke for the beginning hours of the cook and after that it's much more about slow heat to bring the pork to temp vs. smoking it the whole time. This is also because smoking can quickly go from adding a nice flavor to adding a lot of bitterness and unwanted flavors if you overdo it.

So TLDR, wrong cut, wrong amount of time, and wrong temp.

As moscafj's answer correctly states, the lowest average temp on that grill is more like 180-200F so you annihilated that poor bird! Even though the final temp may have been 150, it was almost certainly much hotter than that at some point (if the internal meat was firm and white this is certainly the case). But also, the idea of "low and slow" for BBQing is because your typical BBQ meats, like pork shoulder and beef brisket have tons of connective tissue which breaks down over time, along with tons of fat which keeps things moist throughout the cook (because it slowly gelatinizes into deliciousness). Skinless breast has none of that and is notoriously hard to keep moist regardless of how you cook it.

So really unless you know what you are doing it's a horrible cut of meat to smoke -- and it certainly should never be smoked for that long regardless. Whole chickens should be checked after an hour with an average smoke temp of 200 and will probably be done by 1.5-2 hours.

Additionally, apple wood is not a super strong flavor to begin with, but it's also important to keep in mind that smoke adheres and penetrates the meat best when it's cold and stops "sticking" to the meat once the outer layer gets fairly warm (and pretty much stops doing anything good after 130-140). Given the grill temp you would have hit that fairly quickly and thus the smoke really was only flavoring the meat for ~30 mins. This is why when you are smoking something like pulled pork you are only trying to get the good 'blue' smoke for the initial hours of the cook and after that it's much more about applying low and slow heat to bring the internal meat to temp -- you really don't want to be smoking it the whole time. In fact, it's often bad to do so because smoking can quickly go from adding a nice flavor to adding a lot of bitterness and unwanted flavors if you overdo it.

So TLDR, wrong cut, wrong amount of time, and wrong temp.