That's a fairly common occurrence for D2 owners so no embarrassment in this company
Did the mechanic verify there was no fuel in the tank, or did he simply assume there wasn't based on none getting to the engine? There are a bunch of seals in the pump assembly and if they fail it can suck air at low fuel levels which will obviously cause the engine to stall.
Also, if the pump has been replaced its possible to misalign it when it goes in the tank. That typically causes it to stop at ~20 litres remaining.
Finally, if the pump has been replaced and the return hose not put in to the swirl pot where the pump lives (ie just left loose) it can run out at about 1/4 tank.
Of course it is entirely feasible that one of the two fuel level senders is faulty, but pump problems are the most common cause of this scenario
