That PI call on Smoot was iffy, for sure. Probably should not have been offensive PI either, and most likely should have been a non-call. Smoot's head was turning towards the ball, and contact was initiated by both players. IMO, it should have been a play that the refs shouldn't have interfered in at all.
For anyone wanting to dissect the minutiae of the rule to make their case...
NFL Rules Digest: Pass Interference