I think that the real problem is that he's frustrated. He wants to win, he wants to be #1 and he's used to being treated that way. I think that he honestly expected to be the #1 runner for Oregon this year. As it turns out, he hasn't had a part of being part of a team environment. Instead of it being all about him he's just a piece of a bigger puzzle.
Add that to the adjustments that every normal freshman has (being homesick, classes, lifestyle changes) and it all adds up to his reason for leaving.
He doesn't feel like the environment that he's in is helping him to reach his potential.