During a fumble the player is not in control of the ball, and therefore, cannot be called for a traveling violation. A fumble is the accidental loss of player control when the ball is unintentionally dropped or slips from a player’s grasp. After a player has ended a dribble and fumbled the ball, that player may recover the ball without violating. Any steps taken during the recovery of a fumble are not traveling, regardless of how far the ball goes and the amount of advantage that is gained. It is always legal to recover a fumble, even at the end of a dribble, however that player cannot begin a new dribble, which would be a double dribble violation. A player who fumbles the ball when receiving a pass may legally start a dribble.
Ok, so all in agreement that this should have been a double dribble ( a fumble per se at the end of the original dribble) HOWEVER, again - just like the 75 % incorrect calls on the jump with foot out of bounds to save - I think the ref was watching the hand check/grab and therefore did not see whose foot the ball hit off. If he did not see it, then he cannot responsibly make the double dribble call.
Just my theory based on refs only being able to look at one thing at a time. Same with post travels. Ref is locked in on whether defense is committing a foul or not up top, offensive player can switch pivot feet 2-3 times without notice sometimes.