s don't get many offensive rebounds on a per possession basis. Opponents don't get offensive rebounds while BYU does get defensive rebounds, largely because they fear BYU's transition game.
You have a point that BYU gets more total defensive rebounds in part because of its fast tempo. But rising to the #1 team in the nation in defensive rebounds is new, and it is due to a profound change in defensive strategy by opponents to prevent transition baskets by BYU.
This strategy to give up the chance at offensive rebounds by sending 4 or even 5 back after a shot proved effective last year because the Cougars had such an ineffective half court offense. Coaches are committed to changing that.