Probably looks like semantics, just to be clear, at no stage were both FDs selected OFF. The PM simply turned the PFs OFF. For reversion to SPD mode they both have to be OFF at the same time, prior to the PMs being selected back ON.
The NTSB makes mention that the PM "loosely followed Asiana's informal practice"...
BTW I've mistakenly said the PFs was left ON above, not that it materially changes the outcome. No both OFF, no A/T wake up....