I've seen statements that they determined the goaltender had enough possession for the whistle as their was a delayed penalty on the play, which is what the end result was, USA Penalty for tripping before the goal. I did not see the play yet, and IIHF needs to release a statement like the NHL PR does relating to review decisions. I have never seen a goal overturned due to a whistle should've been blown for possession on a delayed penalty.
Edit: Just went backed and looked at it, I doubt possession was reason for overturned. I can see goaltender interference being called as goaltender was still in the crease, even if it was only one leg.