DaikonNairu -Ren-
So you just default to religion? If the context of the conversation is neither religion nor ethnicity you'd still default to religion?
Well, usually there is a context. I can't think of an occasion where somebody just said "Hi, I'm Jewish!" with no context or hint as to what they meant. I'll be honest, the person's appearance sometimes factors in too, even though I should know that's not an accurate way of judging. I mean, a lot of people have thought I'm Jewish based on appearance.
Though, the easiest thing to do is just ask "Oh, so do you practice Judaism?" That's what I usually do, because it's a polite way of getting them to say "No, I'm just ethnically Jewish" or "Yes, actually I'm a convert to Judaism, not an ethnic Jew" or whatever the case is.
Because I'm nosy like that.