A critical clue will also be the position and direction of the gash.

Were you previously aware of a problem?

Brake Rub would be just above the brake track, and generally following the track.

Rubbing on fender, or other part of the bike would also be obvious, with signs of rubbing following the direction of tire rotation.

Glass might be a very localized problem, at least partial clean cuts through rubber and threads. The direction probably won't follow tire rotation.

Blow-off may not have any tire damage.

I've also had rusted tire bead wires on old abused tires.

Overpressure? Generally there should be a fair amount of redundancy in tire design.

Tread wear through and skidding would be obvious.