In fairness, according to the translated statements, the F/O testified that there were no source for fire or ignition in the cockpit prior to the fire; and the Captain explicitly testified that neither he nor the F/O were smokers.
3. Conclusions (p.66) [ ... ] The cause of the fire could not be conclusively determined. It is not yet known whether the oxygen system breach occurred first, providing a flammable environment or whether the oxygen system breach occurred as a result of the fire. Accident could be related to the following probable causes: 1. Electrical fault or short circuit resulted in electrical heating of flexible hoses in the flight crew oxygen system. (Electrical Short Circuits; contact between aircraft wiring and oxygen system components may be possible if multiple wire clamps are missing or fractured or if wires are incorrectly installed). 2. Exposure to Electrical Current