In your example, you are correct. However, that is irrelevant for this exercise.
The issue being raised is that people are hearing a female voice speaking in a way that is (typically) the way a man would speak. The points of contention here are the adjectives sorprendido/a and enojado/a. No nouns are involved here so your point about the word falda does not apply.
When a person is describing himself/herself in Spanish (and other languages), then the subject is the speaker and the adjectives (which apply to the subject) should agree with the gender of the speaker, where applicable (because some adjectives are the same for masculine and feminine).
A female individual who wishes to convey the message from this exercise would usually use the words sorprendida and enojada because those are the feminine nominative singular forms of those adjectives. Thus it can be confusing when a voice (that sounds like it comes from a female human being) "describes herself" using the masculine nominative singular forms of adjectives.
You can always "explain" this discrepancy by stating that this is simply an unforeseen circumstance from the perspective of the course and content developers, i.e., that the female voice was randomly chosen to deliver a sentence that would be expected to come from a male source. However, that does not address the fact that it can still be confusing to new Spanish learners who see/hear the discrepancy.
I went with “I am surprised and annoyed”, which was marked wrong. I’ve reported it since ‘enojado’ is translated as ‘annoyed’ on two websites (WordReference and SpanishDict). Honestly, I’m surprised and annoyed that this should have been marked as wrong.
Hovering over the words in the sentence, I unearthed something. The sound was normal for all of them except the last. For "enojado", it was pronounced two times, almost completely overlapped. A bit creepy, like a legion of upset creatures react.
Leaving that browser tab and returning a few minutes later returned to a single voice. It looks like the other calmed down. 2018-08-09, Firefox.
No, they shouldn't. Duo is best when it accepts the idiomatic expressions from multiple dialects. If your post starts with. "in my country..." it's probably a bad post. If you want something added, report that your answer should be accepted. If something sounds wrong in your dialect of English, it very well may still be gramatical, whether or not you would use it in he UK.
tobybull...The woman who does this course often is a little indistinct. She often leaves out the final 's' and runs words together. Although it's a bit annoying sometimes, I think it's likely to help us when we are talking to people we meet in Spanish speaking countries who do not always take care to enunciate properly. The man, on the other hand, is very careful to enunciate clearly and I have rarely, if ever, had a problem hearing what he says.