Their premise is somewhat off the track.
Under the right circumstances just about everyone can find fulfillment in any relationship. However society tends to push the traditional relationships on children virtually from infancy.
For some the traditional views simply do not fit, for most societies pressure limits the ability to choose or experiment. Far too many find themselves trapped by their cultures taboos and they spend their lives wondering what is wrong with them. For many societies pressure leads them to a fulfilling life and they cannot imagine anything else.

It's possible that they're so used to the vast majority of people actively involved in the movement being gay that they wonder if you might be gay too and are trying to help you find your a way out of the closet, I suppose. Odd, though - I've also been involved in the LGBTQ+ rights scene for many years, but nobody else has ever suggested I might not have discovered myself (many straight people, on the other hand, apparently assume that because I'm a vocal supporter of LGBTQ+ rights I must be LGBTQ+ myself, which rather annoys me - I point out that I support animal rights too, but I'm not a rabbit).