I'm glad someone has stepped up and reported the content and Duolingo has (eventually) responded by removing it and apologising. Hopefully that's the thin end of that particular wedge firmly knocked out. In my head, though, JKR is mildly amused and ready with a pithy, witty, and possibly, some might say, slightly mean retort.
(I'm not unsubscribing yet and quite enjoy the diverse content, although I agree with previous posters that Duolingo is at best an adjunct to other forms of language learning.)