If it is a real, valid Idaho DL, all he needs is that. They will see him as a normal passenger, nothing special.
He should leave his passport and any documentation about his status or country of birth/citizenship at home.
(He should not fly out of Buffalo, NY, by the way. Don't worry about the "Real ID benchmark" thing-- ID's from all 50 states are valid for the time being).
Why not fly from Buffalo NY?