I hate to say it.....
The fairing is fiberglass, so no surprise it is gone. If you look at the aluminum skin at the edge of the hole (ie, part of the pressure vessel), it is all bent outwards.
If this were a fatigue crack, I would expect parts of the skin to be bent that way, but not all of it.
I hate to say it, but it looks like a bomb to me. Having seen videos of bomb-tests on airplanes before, I would say, if this was a bomb, the only thing that saved them was luck in where the bomb was located in the baggage hold: the hole is just forward of the center-wing box, and therefore, makes that immediate area of the fuselage one of the strongest structural parts of the fuselage.
If not a bomb per se, then something pressurized (scuba tank, medical oxygen, spare tire) may have blown with less force than a bomb.