Tanimbar
The Press Release causes more problems than it solves, in my opinion. I am not expert in fluid dynamics by any stretch, but logic suggests the following.
It is highly unlikely there was liquid water any where in the fuel system of 038 for hours prior to the flight. If present as ice, then a "picture" of the state of the tankage would suggest that it was present as what? Cocktail ice? large blocks clinging to aluminum? That doesn't jive with the temps experienced by the a/c overnight or well prior to launch from Beijing. Block ice won't pump, and fuel won't "freeze" at all ambient temps. surrounding the flight. If the a/c brought it with on the flight in, that's one thing, but logic again suggests the problem arose on uplift in China. In spec. fuel would be carrying some quantity of water (as ice) in the uplifted batch.
As the flight progressed, this ice would "concentrate" in progressively greater quantities as it settled lower in the fuel system. At some point the siphon starts pulling high enough quantities of particle ice with Fuel such that it migrates toward the engines. Passing into the engines it converts to Steam and causes no particular problem. It may even enhance thrust at some miniscule value. However, it also, as a solid, would "fall out" of suspension and deposit in variable flow areas (due to specific gravity difference) and eventually create flow reduction.
It isn't particularly difficult to imagine this occurring at essentially the same time in both engines, ETOPS isn't foolproof, especially when systems are homogeneous and filled with the (same) Fuel.
I can't imagine what "Unimagined quality" the Fuel possessed to remain so mysterious. Rather than mystifying its audience, perhaps Boeing and FAA should tell the complete tale. A year on with new Physics/Chemistry/Fluidics? Stretches credulity. Just sayin'.
AF