Translation:The public restroom is not private.
What is obvious to one person may not be to another.
I am not an native English speaker, and I have never yet lived in an English speaking country. To do the translation in this task, I went to check if öffentliche Toilette is really the same as restroom. And according to this source, it is. I quote one of the many similar definitions: "Restroom - A room equipped with one or more toilets and sinks for public use." OK, checked. Notice that I only know a "restroom" in person from airports here in Brazil. But then I got marked wrong for my translation. Why?
In another source I then found some needed clarification: "In American English, the term "restroom" usually denotes a public, commercial, or industrial personal hygiene facility designed for high throughput". OK, so to say "public restroom" is not analogous to say "white milk"!
Finally, regarding a restroom not being private, I think it may not be so ridiculous as others are suggesting. People sometimes need to be reminded of the obvious, don't they? By the way, I am reminded of a good book, "On the Obvious", from a renowned Brazilian intellectual and educator. :-)
Context, I suppose. Not all meanings of a word are appropriate for every situation the word is used. So, you could argue that Duo should accept it anyway (potentially letting you learn a sentence that would be interpreted differently by a native German), or you could take this as a lesson and learn from it :)
In what way is this a contradiction? It's arguably a tautology, but it's certainly not contradictory.
A non-pointless interpretation of the sentence might be that it's a public restroom (i.e., open to the public-- anyone can use it) but that it has little privacy (i.e., maybe people can see inside), which wouldn't be describing the same thing.
On Good Friday in 1983 I went into a public restroom in Salzburg, Austria. There were only urinals and a sign on a door with something about knocking to use a toilet.
So I knocked and waited a little while. Shortly, a little old lady opened the door and waved for me to follow her. She led me through the women's side to an available toilet and waited for me to finish. She then led me back. A couple of ladies continued washing up and adjusting their make-up while taking absolutely no notice of me.
Everyone I tell that story to is flabbergasted.
Way back then I went to a public toilet in Munich and in the men's section there was a grandmotherly woman sitting on a chair with the men's urinals nearby. Nobody seemed to mind. I think it was 10 pfennig to use the facility
In the same year I went into a pub in Belgium and the toilets were downstairs. There were two cubicles side by side and just outside the women's cubicle there was a male urinal suspended on the wall so the women would have to wait or brush past the man to get in. This was a public toilet but by no means private.