Jesus you guys. He's lean and muscular because he's got the right balance of lifting+sports (exercise) and diet. Stop making this more difficult than it needs to be. His diet is probably helping him get the best out of training and playing sports. Training and diet is helping him be good at sports. Sports are helping him utilise the nutrition side of thing, and keeping him in shape. There's probably some interaction going on at every level, with hardly anything acting in isolation.
He's balancing things right.