i thought that pattern looked weird in the first picture. what you have there is a jungle corn and not a true california king snake - although it most likely has at least half cal king in it. yes, he's a hybrid - most likely at least an f2.

and don't worry too much about him being 'fat' either. one, it means he's got a good appetite and two, he was obviously cared for. many times when people get things in trade it's the other way around.