He was bullied to the point that he had to spend 2 weeks in hospital, according to his own words.
He might be lying, but it's just as likely that he's 'having my turn!'
That particular incident was the result of him teasing a classmate about their fathers' recent suicide and that classmate pushing him down a set of stairs as a result.
Elon's father has talked about it in interviews. It seems Elon was the bully in this specific incident.
I know kids can be brutally insensitive sometimes, but this is extreme behavior even for a child no?
Yes, mocking a classmate for their parents’ death is extreme behaviour, even for a child. I would not be surprised to learn it constitutes fighting words.