that is not "trolling", that's (pretty bad) harassment. I get the feeling this is a story written to prove a point. Nobody would refer to this as "trolling".
I work part-time at a school with kids ranging from 7 to 16, and of what I've tried to inquire them about the subject(I'm 22 myself, so it's quite easy to go into the subject by mentioning some local websites and memes, kids open up voluntarily very well), it's exactly the online harassing and bullying which is considered(perhaps a form of) trolling. These are exactly the imageboard kids who find it cool to "piss people off". Why? "I dont know. For the lulz". It's like a hobby for some.
I personally find this stuff disgusting and directly relate it to bullying in school. Just because it happens online is not any more tolerable. Turns out many people disagree.