Is there any possibilty that the hull could have failed first, (for some unknown reason). Subsequently the rapid decompression of the cargo hold caused an extreme pressure difference between the bottle and ambiant pressure then the faulty fitting blew off the bottle and the bottle torpedoed out increasing the hull demage.
Along the same lines: A possibly more likely mechanism if one considers the scenario of hull-failure preceding O2 bottle failure, is that some object or objects in the cargo hold were caught up in the outflow of pressure-hull air following the breech. Accelerated in the wave of outflow, an object hits the O2 cylinder with considerable force at just the point where the valve stem meets the flask. Effect of this collision is to break the valve stem or the threaded section of bottle just below it, causing the liberated valve to depart upward on the path observed in the airframe damage. Subsequently the bottle might possibly have remained roughly in place as the pressure released, thrashing around and perhaps tearing out its attaching tethers, until it was ultimately carried out the starboard airframe hole by buffeting turbulence (and suction) from external airflow or by cabin air outflow.