The point of the rule, as I understand it, is so the opponent is not faked out thinking you're fair catching when you're not. However, all the Minnesota defenders seemed to be playing as if the ball was live and there was no fair catch. So I think the refs should've used some discretion and not been legalistic about it. If there was no fairness issue it shouldn't have been penalized.
I also don't like that apparently no ref threw a flag at the time and it was only reviewed after the fact. That is suggestive of a crooked ref that didn't like the play's outcome.
Regardless, it wasn't an invalid fair catch sginal. The rule is this:
The returner didn't "wave". He rotated his left arm in a circle like 1 or 1.5 times below his head. That's not a wave. A wave is moving your hand or arm back and forth.
At the end of the day though, I've always been of the view that if your loss comes down to one play you didn't deserve the win that much.