The fellow I was talking to, turned out to be a messianic jew. A southwestern jew ignorant of anything jewish except for a few tzatzkes the family kept when cleaning out grandmas house. When in college he was recruited by a member of a messianic congregation and at first he had the same reaction any frum jew would have, jews have nothing to do with j, that’s an oxymoron in and of itself, this fellow taught him their idea about being a “completed” jew and he became a card carrying member. I know this, because he actually called me a week after we met and wanted to continue the discussion. It took quite some time, and dozens of emails back and forth to sufficiently convinve him to call a frum Rav in his city (he lived near houston) who he met a number of times, and eventually became a mispallel in that shul. While I agree with the sentiment expressed above, that missionaries, like flies, are best ignored, if approached in a respectful manner, you just never know who might be asking and why.
My encounter took place in 1998, 13 years later we have so many more frum jews, kein yirbu, but unfortunately so many more unaffiliated and worse, jews who mistakenly believe they are practicing judaism when in fact they are practicing xtianity in jewish garb.