Negative. Not each and every Budni/Rewe/Edeka sells the drink, neither in Hamburg nor anywhere else. Even among kiosks in Hamburg and beverage stores outside large cities the ratio is rather small. I would appreciate if a map like Matekarte would at least try to be based on verified data instead of a set of assumptions.

Regarding DB clutter: In total we are currently talking about a few more than 1100 places worldwide that have that tag. I hope the database can handle this.

However, if it is a problem, I can remove the tag for this location. But then I don't see the point in having that tag in OSM and having a map like matekarte at all.