My dad, who passed away back in '03, only once that I can remember ever raised his voice at me. My mom yelled a few times but never anything that bad, and I was never as calm as that kid, so that's saying something.
We don't know the story, but I'm going to give the 16 year old who has a job, and his own stuff the benefit of the doubt, over the woman who feels she needs to scream and yell at her kid to give her money to buy gas. Hell, I've tossed my mom a few bucks here and there when she needed it, but damn, she never asked for a cent when i was 16 and couldn't afford to build a decent PC without getting grandparents money.
And since the stepdad or whatever was really cool and relaxed and the kid and him seem to get along (from the brief conversation), it seems unlikely that the kid is an obnoxious jerk. Stepdads generally dont put up with that kind of thing.