As that video points out, if Fultz is still injured it would make no sense for him to be practicing and shooting before he is recovered. This is why I feel very confident its the yips. Furthermore they point out that his jumpshot actually looks great when he hits that turnaround fallaway. Again, further evidence for yips.
As many have explained in this thread, the yips can be extremely context dependent. A baseball player can make a hard throw from the outfield to third base without a problem if the runner is tagging up, but the routine throw in after a fly ball out is impossible. In my case I had yips with tennis. Easy forehands became impossible for me, but if I had to stretch or run hard for a forehand I stopped thinking and had a smooth stroke.
Fultz has some situations where his shot is fine, like that turnaround. Then, at the free throw line, he looks like someone who has never touched a basketball.
Definitely the yips.