The entire kicking team would have been trained of the "approved signals" during a kick. Any unapproved signal by anyone on the kicking team is considered a fair catch violation. Especially the left hand motion to get away from the ball.
Straight from the rule book Article 3 Section V:
V. Team A’s scrimmage kick is rolling beyond the neutral zone when B17 alerts his teammates to stay away from the ball by a “get away” signal. RULING: Invalid signal. The ball is dead by rule when either team recovers.
His left hand motions were effectively the "Get Away" signal.
I had never heard of this rule, but there is it.
As for if this was reviewable, I believe the rules are all scoring plays are reviewed, and plays near the out of bounds are reviewable. So I think the refs can review the whole play.
For about the 100th time. ALL plays in college football are reviewed by the replay official. Certain plays are considered “reviewable”. Questionable plays that fit into the reviewable category are buzzed downed to the on field officials using a pager system. Then play is stopped and the replay official will review the play letting the referee know his decision. It had absolutely nothing to do with Iowa scoring other than the fact the replay official did not want Iowa scoring there.
As a side note, in college football since every play has to be reviewed, you may not hurry up to the LOS and try a quick snap. Minnesota tried it yesterday and play was stopped for review. Iowa had two chances to try and they took their time each time and play was stopped.