Whenever I use a stand that doesn't require a push back I seem to always get a push back truck coming to push me back. The spot(s) are clearly configured via the options for no push back needed.
So many users asked to have at least a straight pushback option, even at parkings when "None" has been set, that's why there always a pushback truck now.
Because of this, it's not possible to entirely disable pushback now, we might add it as a separate option in a future upgrade.