Have you guys gone back to watch it?
I've watched it probably 30x now.
I know they ruled forward progress... but I don't think there was any whistle that stopped the play. The umpire? (the ref behind the offense) threw the beanie denoting a fumble, but then that was the guy who immediately went to the PA and announced the ruling (without conferring with the other officials).
I admit I have not rewatched it, I don't typically have time to watch a game again. I recall them blowing it dead and thinking it was pretty quick, but I'll take your word that there was not an actual whistle blown.