I don't think he intends to play college ball past the 2018 season, if that, and that depends on how well his Junior year goes as the inevitable starter against:

LSU
Utah
Wisconsin
Mississippi State
(Along with Utah State, Boise State, Fresno State, San Jose State)

If he plays as well as his trajectory indicates he might, he may opt to declare for the draft as a 24 year old instead of waiting even longer if he seems like a solid pick. Thus rendering a red shirt somewhat wasted time not playing, even if he is just the backup this year.