Is it common for religious organizations in Korea to ask special questions to foreigners?

I recently encountered a religious group for the first time since moving to Korea. I had heard stories before, so I had some idea of what to expect, but I was quite surprised by their first question. As a Christian, I wanted to continue the conversation with them in a friendly manner. However, their initial question was whether I was homosexual or transgender. I wonder if it is appropriate to ask such a question to someone you just met. I am curious why they ask such questions and what their intentions are. I am wondering if anyone else has had a similar experience, and if these questions are common.