Not so sure what he's so happy about
I'm sure he was just trying to be a jerk with that statement, but prisons are generally places normal people want to stay away from. There's a reason why the recidivism rate is so high -- other than the fact that a prisoner has basically no chance of getting a decent job once they get out. From what little I've seen, the whole experience probably just rewires you, especially on long stays. Before the US closed all the mental hospitals and let everyone out on the street, that was what patients described too...you just get so wrapped up in the routine.
Unless he's basically spending the time in solitary confinement, he's going to end up hanging out with a bunch of...interesting characters.