To me that was not even close to a fumble.
But I understand why the refs let it play on......they're supposed to.
By letting it play on, there can be a clear fumble recovery and then there may or may not be an advancement of the ball. In this case a TD.
Then, since turnovers are reviewed, if it was NOT a turnover, no harm done. But there would be harm done if the whistle was blown and it was immediately called an incomplete pass.
The refs handled it exactly correctly and the result was also correct imo.