Tanimbar:
Having read the report twice now I concur with your analysis and in particular I'm drawn to the last conclusion. Ice accretion inside the wing fuel pipes over the two flights separating when the high fuel flow was demanded and causing the restriction. Where the restriction is is not clear but the face of the FOHE looks like a good bet.
They say that formation of the ice there was unlikely but don't comment on this being the collection point for ice formed upstream.
I'm sure we will see requirements for fuel feed line purging by high thrust demands coming to an AFM near you pretty soon.