Muffed Punt - TD?

[bossman72]

This happened in an NFL game (I think Min-Chi)

K punts. R, at his own 5, goes to block a defender and is touched with the punt in the back. He goes to recover the ball but muffs it at the 2. The ball rolls into the end zone where it is recovered by K.

The ruling was a TD.

My question: why would this not be a touchback and R retains possession? A kick became dead in the endzone and R was not responsible for the force (since I believe a muff is not a force).

Thanks!