It's pretty well established that Boise State is playing a completely different system than what they have played in years previous. So the defensive staff didn't have a lot of film to watch not unlike the Arizona game.

It's not unreasonable that the Boise State staff saved some looks for the BYU game. And when you can't attack an offense it is not unreasonable to play a more conservative base defense.

Now there are somethings to critique about the defensive coaching in that game, but I don't know that it is "scary".