Dryfire and livefire are two different things. It´s stress to your brain shooting live ammo. An explosion in front of your face, recoil, loud bang, thats stress.
Your brain wants to to do a defensive move to fight the problem. You could be dryfire world champ, but do flinch in livefire. It´s almost always some kind of recoil anticipation, IMO
I think John Lovell is very right, right here: