Dynamite not required
There's been a suggestion that some sort of fire or pyrolytic reaction is implicit in an 'explosion' — that chemical explosives are needed, and scorch-marks will ensue. This is not the case. An explosion is any rapid and uncontrolled evolution of gas. It doesn't matter what the gas is, or how you achieve it.
An explosive is a material which, when detonated, undergoes an extremely rapid chemical reaction involving the evolution of a colossal volume of gas very quickly. Detonation is the process of raising the chemical system above the energy level required for the reaction to take place.
An extremely large volume of gas being rapidly liberated from a fragmenting cylinder is an explosion.
As to the likelihood of fire being associated with an O2 leak, it's not compulsory: if there's no ignition source to hand, there will be no fire. There are materials that will spontaneously combust in pure O2, but we're not likely to see any of those in the hold of an aeroplane.
Finally, yes, a rocketing gas tank would need to accelerate for a few metres to knock a hole in a seam, but that folded-up bit of fuselage is interesting nevertheless. Were there any gas tanks in that hold other than the ones that were (theoretically) bolted to the sides? Any scuba enthusiasts on board?