More speculation but don't we already have a precedent for the ignition source, namely the 227 incident?
Having read the Unit Inquiry Report its seems to be feasible that the same or a similiar chain of events could have occurred on 230:
....damage (Enclosure 1) to XV227 comprised of
heat damage to:
a. The starboard rear spar at the fuselage joint post attachment point.
b. The starboard mainplane lower skin.
c. The forward face of No 7 Fuel Tank starboard and leaking FRS couplings due to seal damage.
d. The SCP duct, duct fairing and associated assemblies.
e. The aileron output cables and associated pulley.
f. The flap interconnecting cables.
g. Various wiring looms adjacent to the failed duct.
That is unless something has been done since the 227 incident to prevent a similar incident!