I worked on HF comms for various aircraft and that oxygen tube with a steel wire inside concerns me. If the crew had set frequency on the HF on the ground, the antenna tuner would have gone into tune mode telling the HF to transmit a carrier, exciting the entire fuselage with RF until a tune solution was set. RF currents in a fuselage are quite strange, and I remember having odd arcing in screen rooms when testing HFs with as little as 100 watts. A coiled wire would certainly have been enough to generate arcing in the tube filled with oxygen. I sent an analysis to Boeing but never heard back. The analysis of the coiled hose support causing a DC short does not make sense as there were not wiring bundles in contact with the hose. An ignition source excited by the HF in tune mode should certainly be looked at.