Zombie Pigmen attacking when not aggravated by player

While I was in the Nether fighting a ghast, some nearby zombie pigmen got hit with one of the fireballs the ghast threw at me and the pigmen got aggravated towards me, even though I wasn't near them let alone hitting them. The only mob i was fighting was the ghast. In a nutshell the zombie pigmen got aggravated towards me (the player) despite me not directly causing them to. I'm pretty sure this is a bug.