Given the short flight time, fire trailing and persistent and the pilot reporting and engine failure.....maybe a turbine burst (looking like engine failure with zero Tq/Nf), That savages the tail boom flange area with shrapnel. Meanwhile the Gas Generator is still working and the FADEC response to Zero NF is to open the fuel to max chat. The fire escaping from the compromised combustion chamber finishes the job. I have no idea why the pilot did not have a fire warning or if he missed this in the mix of confusing indications.
With an engine fully failed (ie all parts stop rotating) the fuel pressure becomes zero everywhere in that firewall box and the chances of a persistent fire almost zero. Maybe!
DB