Touchback or Down on 1

[MJT]

I would think this would be similar to a play where the receiver catches the ball while in the air in the EZ, gets hit and driven back to the 1 yard line. The ruling in this play is if he downed immediately, it is a TD, BUT if he comes down on his feet and continues to fight or run, then down at the one.
Thus, I would say if he goes down on the hit, TB, but if stays on feet, it would be the spot of his forward most progress. So, in your play, he went down at the one, so TB.