True, you may have cooked it too much and spinach is cooked when it reaches 160 degrees F. If the spinach overcooks, it does not necessarily mean it is bad, it is just overcooked. In my opinion, eat it, I have because mine did not taste bad as I understand yours did not taste bad.
Now, another idea is that when you have smelly spinach, you might have cooked in on very high heat and you burned it or overcooked it, you could still eat it. Again, if it does not taste bad, it is ok to eat it.
Another idea is that you used rancid oil, which using the rancid oil on the spinach would taste bad and you would then get rid of it. That would taste bad.
Also there is the problem of listeria, which is some kind of a bacteria, I think, and the spinach is bad to begin with and will or might make you sick. Please look that up, lettuce also has that problem. I think the spinach would have a blackish hue to it and taste bad. Get rid of it.
Lastly, what I read about spinach is that you do not re-heat cooked spinach, eat it cold. I make big batches of creamed spinach, my family loves it, takes it to their homes, nukes it, and nobody has gotten sick. I am no doctor, so take that info for what it is worth.
Lastly secondly, I use frozen spinach to make dips. I make too much of that also and I make my own creations of that. My family likes to take that home also. What I do with any dip is put out smaller portions at a time and fill up as necessary. It is time consuming but as a safety issue it makes me feel good and when you feel you are doing your best to keep people eating safer, it is worth it.
At very Last, use your judgement, don't take chances. When in doubt, throw it out. I do what I do because I have a lot of experience, but that does not mean I don't get into trouble once in awhile. Good Luck