That particular site doesn't exist here. There is a similar site, but not used very much.

Still, for what it's worth, have a look: https://www.meinprof.ch/uni/prof/1431

Vielen dank! Fwiw I totally believe you were telling the truth. :)

Because if there ever were a representative sample of how students feel about a professor, it’s ratemyprofessors.com.

Where else would it come from that is publicly available?

Nowhere, but many universities do have student feedback/evaluation forms that you get back after teaching a class, so a professor could know even if they weren't rated on a website.