Of course what is ( also ) not known ( and may never be ),
is precisely WHEN those prime Pumps were switched on and the XFER pumps switched off.
In the case of losing both engines without warning ( e.g if there was a false reading on the CAD ),
could it be that an attempt was being made to relight the engines, with use of the Prime pumps - as you would if starting up on the Ground ?
Would that be a more likely scenario than a pilot inadvertently operating the wrong switches - switches that they are very familiar with ??
Nail