The impetus didn't come from the defense. Even though they forced the fumble, the impetus still came from the offense. No different than a blocked punt, in which the impetus is from the offense.
No. Actually the rule is pretty specific to/about punts. Maybe you missed my corrected post at #5 on this thread? There is no way on the play in question where it could be suggested that any of the momentum of the ball could be thought to have come from an offensive player.
ML/NJ