I'd expect as much--since you can't refuse service to someone for the stated reason of having the wrong skin colour or religion, you of course also can't refuse service without stating any reason at all. That rule doesn't exist just to protect consumers only from being discriminated to their face.

I'm kind of surprised that this is in the GDPR, I thought it had been part of consumer protection regulations for much longer. Maybe that was only in specific EU jurisdictions.