I ate the best fried rice of my life in Vietnam. The thing that made it so good was these crunchy little bits. They were about the size of a regular grain or rice but they were very crunchy (more crunchy than puffed rice). I'm wondering if this could have been uncooked rice fried in oil. I've tried searching google and can't find anything accurate.
Crust formed on the bottom of the pot deliberately? You put the rice in a very hot stone pot after cooking and let it sit a bit so that the crust develops (Korean version). Or you add some butter up front and cook the rice longer than necessary so a crust develops in the cooking pot itself (Iranian version). Many ways to do this, but I agree it's divine :-)
They could have been individually deep-fried grains of pre-cooked rice. A salad of these are known in Thailand as nam khao tod, and I expect that the Vietnamese have their own version.