My guess it's a software bug., and is probably affecting a whole range of VAG products.
But mainly, who's going to notice?? I can't remember the last time I glanced at my odo !!

You could also do that thing (can't quite recall exact sequence) to bring up the service indicator and see if that's going backwards too.
And from a physics point of view of course you must bear in mind that time
can run backwards, it's just very very very very unlikely. Unless of course you are in a Volkswagen or a DeLorean...hahahahahahahaha