You're telling me what you think the rule should be. (And I agree.) But that's not what the rule is. The quotes I cited both would indicate that this was not a safety, and that this was a touchback. Show me anything (aside from reason) that would suggest that the play should not have been ruled a touchback.
ML/NJ
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.
Wrong. A touchback can only happen on a change of possession -- kickoff, punt or fumble into the opponent's endzone recovered by opponent.
This was a fumble into his own endzone that went out of play... therefore a safety.