He is small by average standards, however, when breeders are not careful about the animals they breed to each other the babies are small. Does he get regular dust baths in dust (not sand)? If you are dusting him properly and his fur still looks like that, I would say he is poor quality which would also explain his size. If he is eating and drinking and isn't boney you don't need to worry. He may not belong on a show table but that doesn't make him any less of a wonderful pet for you.
