Yeah, he should be an even fluffy all the way around. Some chins just fur chew, there's not really anything that causes it. But, if he hasn't been taken care of really well, it could very well be from boredom. I think getting him some chew toys is a great idea. Chin wheels that are safe (15" diameter, solid metal running surface) can't be found in pet stores and are generally pretty expensive. So toys right now are probably the easiest to get your brother to agree to.
If you can only get to the pet store, I would suggest lava bites, lava dots or any of the other Super Pet lava items. My chins love those. Or some of the loofah items that Super Pet carries. Otherwise you can look at the bird section and get some all wood (no rope, rawhide, cotton etc) hanging toys. Most of the small animal wood toys are okay, but do not get the peach twigs, peach is toxic to chinchillas.