"How would you explain every other flight from PEK to Europe that night having no other issues with fuel?"
A quite reasonable question, of course. My best SPECULATIVE answer:
1) Their not having followed the same flight regime (including a host of environmental and operational factors)
2) Them not all being B-777, with perhaps a unique vulnerability in the piping configuration.
3) Their not having received the exact fuel load, from the same reservoir , that BA-038 got
In other HIGHLY SPECULATIVE words, I think that substandard fuel was probably a key factor, but one that needed one (or several) other elements to be in place in order to cause the response that occurred -- partial occlusion of the input lines to both HP fuel pumps during decent.
Again, a complete GC mass spec analysis should be cheap, easy, and definitive.