YT vid
Not sure if that's a whistle or not @ :05
That is clearly a whistle.
I do believe though there is a rule in the NFL (among the 100s of rules like we're supposed to know them all) that if the whistle is blown dead but it's wrong, and there is a clear and concise recover/posession afterwards, the ball is awarded at the spot.
He clearly recovered it in the endzone so perhaps that is why?
I may be confusing this with the NBA though but I thought something like this is true in the NFL too.
But then you have weird rules with the whistle blowing like if it happens after they declared forward progress stopped and a fumble happens and is recovered by the other team, the forward progress call takes priority over everything.
EDIT:
But then they ALSO have rules where the offense can and can't move the ball forward on a fumble recovery, and I thought you could not fumble the ball into the endzone. So I have no clue really lol.