"When a player is in control of the ball and attempting to pass it forward, any intentional forward movement of his hand starts a forward pass."
Based on that it was a forward pass as soon as Mahomes' hand moved forward. The fact that it was knocked out of his hand doesn't matter. (That's not what I thought when I was watching the game. But considering the way the rule is written I think they got the call right.)
AlbaNY_Ram
