This probably wouldn't be one of the first sentences i'd use when speaking with someone in Poland.
The matter of translating Polish "człowiek" to English "person" is difficult. I wrote something about it here: https://www.duolingo.com/comment/19428542
I think this is one of those situations when I wouldn't accept it. "Jesteś człowiekiem?", after all, is like a phrase from a sci-fi movie.
After reading your other, lengthier comment, I still don't see why "person" is marked wrong here. "Are you a human" and "are you a person" are both strange questions, like something one would only hear in a sci-fi movie. And you say in your other comment that człowiek is more commonly used than osoba. Well, "person" is more commonly used than "human" (especially as a noun). So, again, why wouldn't it be used here?
I discussed it with a native that helps us regularly, I actually expected her to agree with you, but she's against accepting it. Basically, "person" and "człowiek" overlap, but are definitely not the same. A person doesn't have to be human. Okay, obviously we enter sci-fi mode now, but if an alien asks you "Are you a human?", this alien is clearly a person as well but not a human. Similarly in comics/animations with antropomorphic animals, they are persons as well. I know that rejecting 'person' annoys many people, but I still think it's worth pointing the difference between "człowiek" and "person".
I'm still a bit baffled, but it's a pretty minor point and I appreciate your diligence. I can live with bafflement.
Person would be "osoba" I believe just like in serbo-croatian btw...Polish is a piece of cake for a native slavic speaker like me :) Just the use of the instrumental case with the verb "to be" is a bit bothersome for me, gotta get used to it...
I still find these examples very useful for learning how to structure my own sentences that make sense...
So this is what they meant by "far-fetched sentences" hahahhaah... this is indeed a strange question to ask.
I came across "Jesteś Kotem?" earlier. That is indeed a very useful phrase to learn
Professor: Amy, what are you? Amy: Human. Professor: Damn!
Sorry to like most of you since this show is ridiculous.
Have you heard the Text To Speech audio? We're still safe, they won't sound natural for some time yet ;)
Wygląda na to, że jeśli jesz mięso, jesteś człowiekiem. Jeśli nie, jesteś wegetarianinem.
Just a little joke, because I just came across the "humans eat meat" sentence. I am a vegetarian myself; don't have a cow! ;-)