Not sure I agree, based on the initial post.
1. Player jumps and while over the EZ, grasps the ball.
2. Defense carries him out of the EZ to the B1.
If the play ended there, then yes, touchdown. But the post says, "turns and attempts to get back in the end zone". That phrase implies there was no forward progress, the receiver broke loose from the defense and was again on his own. If so, he's down at the B1.
The case play assumes the receiver never regains his feet and attempts to advance on his own. If you judged he did, there is no forward progress in the end zone.
If a player breaks loose from an attempted tackle in the field of play before forward progress is called, he doesn't get the spot of furthest advancement, he gets the spot where he is downed. Nothing different here.