I was thinking of A bi Gezunt, and that’s always what I thought it meant (so it should be, you’re healthy). I am happy to have the more correct translation. As to why i would answer if I don’t speak Yiddish, well I don’t speak French, either, but I still know what some expressions mean.
You can learn a lot about foreign languages just by listening and observing. As an example, here are some French words and expressions that I picked up: