"The people camp in the winter."
Translation:Hoʻomoana ka poʻe i ke kau hoʻoilo.
A little more explanation of your question would be helpful. Are you suggesting that the sentence given by Duolingo has an error? In this sentence, using the "ka" determiner is not referring to one specific person, but is talking about people in general. Using the "nā" determiner would suggest that you are talking about multiple people - I'm not sure, but I think you might also be able to use "nā" to refer to people in general. If that's true, then either "ka" or "nā" could be correct in this translation.
No error in either of Duolingo's sentences here, Hawaiian or English. But often when I write "ka po'e" it tells me "nā po'e" is "another correct answer." If for some reason "nā po'e" is wrong here, it should says it's wrong, not just a typo. (What? I accidently typed "n" instead of "k" and then "ā" instead of "a"?)