He's killing it right now—his star is rising at BYU, and there's no reason to think that a USU program in shambles is the best option he's likely to get.
If he does this for another year or two, P4 opportunities will become a real possibility.
If he's ambitious and wants to climb ladders, I think he goes farther as a BYU coordinator than as a head coach at Utah State.
My personal belief: He's happy where he's at, and is just fielding calls to stay sharp as an interviewer and get a little leverage for salary negotiations with BYU.