I hate to bring up a bad memory, but it is a little similar to famous 4th and 2 play
In that case, Kevin Faulk caught the ball past the sticks, but bobbled it in midair, just a little. The defender was pushing him backward toward the LOS. Because of the bobble, the ref did not give him full forward progress, only progress to the point where he later re-secured the ball and got two feet down. That was (in the ref's opinion) just short of the line to gain. Kevin did not fumble, but he lost control and that affected the spot, to our chagrin.
Here the player caught the ball, lost control of it before crossing the goal line, and then needed to re-gain control in the end zone with two feet or a knee down for it to be a touchdown. Also in this instance the recovery was taking him to the turf, so he needed to maintain control as he landed. In this case you do have to call it a fumble, since he lost control and NOBODY gained control in-bounds. It has to be treated like the famous Leon Lett fumble out of the end zone in the SB vs. (I think) Buffalo where he was caught from behind at the 1 and fumbled out of the end zone.