As a witness you were expected to announce your belief like a trumpet toot to all and sundry. Witnesses also tend to believe they had a license to ask other people including complete strangers to explain even justify their beliefs, because, apparently, when you believe you are right and have all the answers you have a right to ask and know because you are on a mission from God to put people right.
Now, I view this rather personal question as a trap. The sort of question one asks right before they give you what-for on how wrong or stupid your beliefs are. So, because of my distrust of the question I tend not to ask people what they believe re religion anymore as I feel it's none of my business and what I believe is none of theirs. The only exception to this is if they state upfront why they're asking (but even this can be a trap) or I know them very well.
Call it once bitten twice shy, but, there you have it.