We know AJ had 156 yards rushing in that game. The sample size is small but against Tulane he had 40 and UT Martin 37 yards. Decent but not spectacular.
Against AZ the NM QB, Dampier, had 130 yards rushing. Against Auburn 17 yards and Montana St 34 yards rushing.
Again, small sample size and maybe they just didn't want their QBs running and risking injury against FCS teams.
Plus, BYU hasn't done very well against mobile QBs yet. But maybe, just maybe, we're better than AZ?