Zombie pigmen will redirect their anger towards you after killing a different mob

I was in the nether fortress, having little luck getting wither skeleton skulls. there was a skeleton that i was fighting, but had to step back as pigmen were getting in the way. the skeleton shot the pigman and they all got angry at it (as normal). however after the skeleton was killed by the pigman all except the one that had been shot by and killed the skeleton got angry at me. i would have died in the lava below if i hadn't opened the world to lan with cheats, denying it as a legitimate death.