Don't healing items always go first, before the attack?
Ok here is what I think happnened.
At a certain point of health, the NPC'c will heal their Pokemon. Lets say that response is at 15HP>. If they survive at a higher HP, then they attack, if you hit them at the correct 15>, then the game will make them heal their Pokemon.
Two things.
He went first the next turn... eg. Accelgor VS Carracosta, Accelgor attacks, Carracosta attacks, Accelgor heals
Your game is glitched...