If it is an uncontained fuel driven fire, that will be like a blowtorch so no wonder the TRDS and tailboom gave way.
Talking of possible blowtorches, the hydraulic line connectors are directly above the connecting flange, with fluid at a far greater pressure than fuel.
(Hyd@103 bar / Fuel press caution @ 0.6 bar P/W, 1.3 bar Arr2B1)
Effect rather than cause of fire?