SLF may have found a clue here...
Japan branch officials of China Airlines said a ground maintenance worker noticed fuel leaking from the back of the engine after the aircraft had landed. "
Flight data recorder possibly might have the answer as to the fuel HP valve and/or tank valve positions.
If the fire damage to the engine is not too severe, lines/fittings may well be suspect as well.
Sometimes the smallest clue will lead the investigators in the proper direction and if faults in the design are found, it could have rather serios implications, as a lot of these acft are used worldwide.
Full marks for the crew for getting everyone out in time, and...this should put to rest once and for all the idea in some narrow minded CC (mostly based in Europe) that so-called 'foreign' airlines have less than desirable safety procedures and training.
I have personally (many years ago, from a parallel taxiway) watched an evac of a CI B707 at MNL after a heavy landing and subsequent fire, and the CC performed superbly in getting nearly everyone out in record time.