Time for a rant:
I do not think this story has anything to do with middos.
Do you think that a 20 year old with a proper self esteem would treat a “slow” person like that? I do not.
So these kids didn’t have bad middos, they had bad self esteem, which could only be fed by taunting someone who they could perceive as lower than them.
I don’t think they are bad kids, I just pity them. And pity their parents and rebbeim who messed them up so bad.