Health/sanitation law is intended to stop people from getting sick from restaurant food. If you get sick from restaurant food, that would universally be considered a bad experience (and for those inclined, a bad review). That's a direct counterexample to the GP claim that there's no agreed-upon way to distinguish "bad" and "good" experiences.

I still fail to see why anyone thinks this is relevant. I agree health law exists for the purpose you cite - and this fact is not related to why patrons in the study give bad reviews of restaurants that are actively operating with permission of the health department.