You don’t owe a stranger an answer just because they asked a question in public.

Being asked something in front of other people can feel like a summons, especially when silence would look rude. Asking is not the same as being owed, though, and an audience does not create an obligation. Your reasons, your plans and your private details stay yours to release or keep.

Practice a short non-answer you can say pleasantly: that is a long story, or I would rather not get into it. Say it without hurrying to fill the pause afterwards. Most people move on immediately, and the ones who push are telling you something useful.