It doesn’t matter who the Gerber Baby really is. Society has chosen to associate the Gerber Baby with certain attributes regardless of who the person behind the photo really is, and so it is with Kevin Mitnick. Mitnick, the real person, excelled at social engineering more than any other trait and was arguably subjected to malicious prosecution. But in his later years, there’s a lot of documentation online indicating that he didn’t live up to the myth that grew around him and he was not a pleasant person [1].
People here are mostly reminiscing about Mitnick--the myth, not the man.
I think we'd all be surprised to find out how many "legendary", "amazing", "revolutionary" famous people are not particularly pleasant. You don't achieve greatness by being a sweetheart.
[ftr, I have no idea what his demeanor was; like many, it's quite likely he softened over time.]
Regarding your source: People don't behave consistently all the time. There are probably people who have briefly met you when you were not in a good mood who would say that you are a jerk.
I don't really want to say bad things about someone I respect who just died, but the fact of the matter is that Kevin (especially when he was younger—he mellowed out later) really could be menacing. Combined with the compulsiveness of his nature, that could be unpleasant. It was as if he could not stop hacking and messing with people.
RIP dude.