Because of the same rules, German restaurants also get to pick and choose which reviews stay up. They can literally take down any specific reviews they like.
A restaurant that mostly gets 1 star reviews will still show up with 5 stars on Google maps, as they will simply delete the reviews with less than 5 stars as defamatory.
Here's a couple of examples:
https://www.reddit.com/r/germany/comments/1peujau/google_rev...
https://www.reddit.com/r/germany/comments/18z4shs/legal_thre...
https://www.reddit.com/r/frankfurt/comments/1lox7ha/bad_revi...
https://www.reddit.com/r/germany/comments/1iiaco8/restaurant...
https://www.reddit.com/r/AskGermany/comments/1ha7sxf/why_do_...
https://www.reddit.com/r/SipsTea/comments/1t613w7/it_was_fin...
https://www.reddit.com/r/germany/comments/1l98608/threatenin...
https://www.reddit.com/r/germany/comments/1sw34jc/can_you_ge...
https://www.reddit.com/r/germany/comments/1sw34jc/can_you_ge...
https://www.reddit.com/r/germany/comments/10kmn66/writing_an...
tl;dr Germans are particularly bad at coming up with reasonable rules to handle these situations