Ok, for a second put yourself behind the plate...
The batter jumps out to bunt.
The pitch heads towards the batters head.
The batter to avoid wearing it, jumps back and you hear a thwack!
The batter heads off toward the dugout like he has been hit. You think he has been hit so start to raise your arms to call dead ball and glance at your crew (Our local mechanics say when a player gets hit all field umps that saw it signal as it is often difficult to see from behind)
Your crew is not signalling dead ball so you realize it didn't hit him (he is just acting like it did) just as you finish opening your fists for the 'dead ball' and you see the catcher pick the ball up just in front of home plate (foul - is based on where it settles so it isn't foul)
If he had not opened his hands and instead dropped them to his side would the play have been that different? Did the runners react to the umpire or their batter?
Watch it again at normal speed...