not sure how much oil it holds but i can give you an explantion to why it could be different amounts....
because Audi are trying to get as many cars in and out of the garage in 1 day as poss, instead of undoing the sump and let the oil drain out, instead, they put a oil vacum into where the dip stick goes and stuck the oil out and they top up to fill levels..
(im not a fan of this way as i like to drain it empty as all the crap comes out in the oil)
that could be one reason.... or the other could be they are trying to ripp you off!! (the guy in the garage could of dropped a litre and charged you!!)
Cheers