The funny thing is that Indy isn't a big team either, so their offensive rebounding is a bit odd. My guess is that the high rate of quick threes they shoot leads to longer kick outs, which generally benefits the offense.
I don't get to watch Indy that often due to being in their market and not getting their League Pass games. Do they scheme to crash the boards on offensive possessions, too, instead of getting back? That would also help explain some of the poor transition defense.