Marc,
The back cover ( Vanagon Quick Data) of my Bentley book calls for 4.5L (4.7 US qt.) for the water cooled-motors when the filter is changed.  I'm not sure if an extra 1.3 qts. would do much harm or if if they would fit in the motor.  If the tech checked the dip stick when he was done he would know he overfilled the motor.  My guess is that the motor was not filled or checked and that they just guessed at 6 qts. when they were doing the bill.
Good luck,
George
'85 Westfalia