A couple of times I’ve been taken aback at what I heard customers say at their table. The reality is that wait staff can overhear without trying and will talk in the kitchen, though most try to not be too critical of those leaving us tips.
The story in your link shocks me. Bartenders usually keep their mouths shut-it’s part of the job and restaurant owners respect customers.
I was a bartender for 20 years...10 of those at a country club full of doctors, lawyers, judges, etc. People would be shocked at the things I’ve heard. And I never said a word to anyone. Wouldn’t have even thought about repeating any of it. This just blows my mind.