Agreed Henry, IF the cad had completely failed you wouldn't know it wasn't empty. Until we know more about the error code then it is a big IF.
CAD fail, Red Low Fuel would surely make anyone with system knowledge check the Xfer pumps are on, regardless of RFM procedure.
Perhaps that was the trigger, and as Art guesses the wrong pumps were turned on whilst his mind was on where to land.
Art - Do you know how much Fuel the engineers physically drained from the supply tanks? I'm guessing the supply QTY was showing zero?
Disregarding the drill in the RFM? What is the drill for CAD failure and subsequent loss of fuel qty indications? Maybe wrongly it assumes Xfer pumps are on.
FS