There's a high school variation of the rule that says on a deflected ball (like the one last night), the offensive team can possess the ball in the back court without it being an over and back violation as long as the offensive player who first touches the ball is in the back court when the deflection happens.
Even in high school with the modified rule, it would and should have been an over and back call because all 5 BYU players were in the front court at the time of the deflection.