Most important statistic: score
2nd most important statistic: turnover margin
BYU has absolutely DOMINATED both of those 2 statistics. That is not just good D, but O and ST are not turning over the ball. Keep winning that statistic and BYU will win most games.
BYU won TO margin by 3 in 2 games, 1 in 2 games and tied in 2 games. Not lost TO margin in a single game.
Add in 4th downs/ turnover on downs and BYU won 4th down conversion 5 games, most dramatically and tied 1 game.
The combination of both TOs and 4th downs BYU has won literally every game. Most were quite lopsided.