If the creampuffs don't count, most BYU QBs had tepid records. The bottom line is he played well enough to win. That's what we ask for. To say he was an ineffective QB because he had a great record against weak teams doesn't really make sense to me. It might be an argument if I was claiming he was a great QB that powered BYU to a very impressive season, but I'm not making that claim.
And, FWIW, he didn't start against NMSU, Heaps did.