Actually, we haven't been the greatest at defending the pick and roll. Usually Ibaka bails us out with his shot blocking ability at the rim. I can't see the videos at work, but from what I remember, Ibaka was on the bench and Kanter was in the game during the pnr dunks. Kanter isn't much of a defender, so it's a believable result. Giving up two dunks to the same guy in a short amount of time might be a little head scratching, but I don't think it's a ridiculous result.
It'll be interesting to see how the pnr defense is after a few days of playing. Then we'll be able to make a better verdict.