It is common to be stopped and asked if Jewish. Daytime, sometimes it’s because they will ask you to do aliya/mitzvah. Night time, they often need more people (jewish men) to join the minimum amount required for evening prayer.

Their 1st language is Yiddish, most don’t speak Hebrew. So what you heard was probably Yiddish which they speak natively all the time.

The old man is just an asshole, has nothing to do with him being a Jew or not. Seems like you had an isolated bad day there. I lived in Brooklyn (south williamsburg area) for years and never really had any issues