Absolutely absurd that it wasn't looked at again. Was it a fumble? Yeah, probably. It looked like the ball was out of his hand before his arm came forward.
But you can't take 2 minutes to look at it again, with your referee, and make it official? Instead, you get Al Michaels curiously telling millions of people that upstairs "confirmed" it was a fumble. So when plays get reviewed on the field, is it ONLY the replay official that has any input? Obviously not, as if that were true, there'd be no need for a booth on field for the ref.
There's just something bizarre about this ending. I hate it, immensely.