I wouldn't fuss about the technical nutrition stuff. You will hear different things from different sources. There are just as many health kicks around now saying high protein is best as there are that don't say that.
I'm thinking the kid doesn't want to become Arnold Schwarzenegger overnight, so he doesn't need a special bodybuilding diet. The best way of eating is following Natural Hygiene principles and having as much raw as possible. He already has a lot of raw by the sounds of it, so if you could introduce him to the idea of combining his meals and having fruit only in the morning he will be getting the most from the foods he does eat and there will certainly be enough nutrients in his body to build the lean muscle he is working on. Get him to research Nautilus bodybuilding too, it's far more efficient than traditional weight training.