Last week I was picked on by a troll on here, and I still haven't found out what it was revenge for. How can I find out what it was revenge for?

I hadn't previously done anything to piss that guy off, he just swooped on me out of the blue and falsely accused me of being someone else. When I told him the truth who I was, he got worse and started bullying me, but nobody has found out why he picked on me to start with. How can I find out?