Maybe he is just picky and is looking for the freshest pieces? I think it is pretty typical that chins don't eat the entire pellet. They will eat part of it and throw the rest away. Hopefully you are feeding just a pellet diet, with no junk food in it. Also, if you are providing plenty of hay in addition to the pellets, I would think he is fine. Do you weigh him to make sure he weight is stable? That is one of the first signs that something is off with your chin.