Yes. Hard to attribute Gunner muffing a punt to the defense who forced that punt to begin with. I guess you could say the same about FGs, though. If we do that then the Pats defense has a point differential of 0.So it counts opponents' drives that ended in a FG as a score for that opponent, but not the drive that ended in a Gunner muff recovered for a TD by the Jets?
A more sophisticted metric would incorporate field position and turnovers. One could credibly argue that the Pats defense has a positive differential because they are even on TD scored vs allowed and the Pats offense has punched in a couple of short-field TDs after turnovers forced by the defense.