The obvious answer any reasonable and decent person would give would be - 'I don't know and it is none of my business'.
However, it is also rather easy to see from common sense observation that it doesn't seem to be a choice for most people. Still, we can never know for sure other people's mental state.
Finally, anyone who stresses this rather pointless distinction is a busybody and a bigot. So what if being homosexual has something to do with role models or abuse (an absurd notion, but not impossible)? The point is that being homosexual is not 'worse' than being heterosexual, and if you think it is you're an intolerant bigot.
Please apply the "mind your own business" part to religious discussions on your part as well.