The complaint isn't about a friendly wave. The complaint is that it's someone's turn to go, and instead of going they wave at someone else to insist the other person go out of turn.
The wave is an insistence of "you go first", not a greeting or a thanks.
Traffic isn't just 'other cars'.
> The driver has the following responsibilities: (...) to do his utmost to ensure that other road users are not endangered, especially the most vulnerable (pedestrians, cyclists and electric scooter riders)
There are definitely places where letting someone go is appropriate, especially if it's leaving a gap so they can make a turn. But if you're on a road and you have to wave them through then most of the time you're not actually helping, and fake-helping is an annoying thing.
Hell, doing it is even an official recommendation in my country: https://mobile.interieur.gouv.fr/Archives/Archives-publicati... ("faites un petit signe de la main" = to wave)