I mean, Forest used to be a place where Groups of Gankers hosted and invaders tried to kill them, teaming up with someone if necessary.
Sometimes there were even some so honorable they refuse to team up to beat Group of Gankers, they wanted to do it alone, to show the don't need help.
But I was alone. I wasn't even trying to summon, I just wanted to kill Sif.
I think Forest Hunters became the monsters they tried to destroy.
PS: Most of them attacked while I was killing the Forest NPCs too.