It kind of does have to be that way. Despite the lack of articles, definiteness and indefiniteness can be expressed in existential clauses with word order and, when there's a plural subject, with grammatical case as well. When the existential clause begins with the subject, i.e. the thing that exists, the subject is definite. In other words, "Tuolla on kenkä" translates to "There is a shoe (over) there", whereas "Kenkä on tuolla" translates to "The shoe is (over) there". Here we have a plural subject, so grammatical case is another factor. The nominative plural form used here indicates definiteness, whereas the partitive plural form, which would be "italialaisia kenkiä", would indicate indefiniteness, i.e. just "Italian shoes" without the definite article.
the problem is, whenever anything like this turns up, you never know if it is one of Duolingo mistakes again or it's actually right. Because it does have a LOT of mistakes (I judge by the languages I am fluent in or am a native speaker of). But when you're studying a language, you don't know if that's the case. Like, it works the same way in Russian (for the same reason), and they never get it right.