You need to make sure that you are picking the correct instance of the enemy. In your case you should tag enemies that have been hit (with a boolean or something), and only change the animations of those enemies.
But I think you are overcomplicating this. Are you trying to show hit damage on the enemy by changing their animations? If so, you should keep a variable like hitPoints on each enemy. Deduct 1 from their HP when hit, and then set their animation based on their HP.