I Assumed that Leon Was Sully's Dad

I guess so. Leon didn't seem the kind of person who'd abandon his kid. Plus, in the scene where he approaches Dushane to ask him to leave Ra'Nell alone, he barely even acknowledged Sully not Sully him. Again, Leon didn't seem someone who'd do that to his kid.

So it just seemed to me that Leon grew up in those apartments, was a former dealer himself and just knew a lot of people.

I don't trust people who don't like pets and I don't trust people who pets don't like.