>>281167691>>281167073While there is a bit of room for ambiguity there, the no at the end there is more likely to make it a question than the other meaning of softening a sentence. If you look at the comments on the JP chapter:
https://shonenjumpplus.com/episode/17106567267987413267
There was someone who also understood it as a statement, but others mention how it is very likely a question, showing that most actually Japanese people also got it as a question.
It also makes more sense with how the chapter goes. If she meant she met a dragon, you would likely have seen Ruri or someone else there at leas thinking about it, even if they don't ask her for more information. Airi hit her because she was being impolite with many questions in a row. And Ruri asking about her dad to mom also makes more sense if that part earlier was a question, as another person asking Ruri if she ever met a dragon, and her dad being the obvious one she could have met, making her thinking about meeting / wanting to learn more about him.