You are the expert in your own life. Sometimes people who are used to being the expert in their craft don’t know how to trust you about yours, and in their defense, they talk to a lot of people who don’t know what they’re doing. It’s still their responsibility to do their homework and not let their biases and assumptions get in the way of doing a good job.
This incident came up recently while I was on a book panel for asexual authors. When asked to discuss the publishing process, I told this story–about how an agent I queried assumed I made up asexuality and was trying to start some new thing, and how the sales would really depend on whether I could get my book to the necessary audience. The whole interaction was pretty yikes. When I found an agent who actually told me how much she thought the book would help people, I knew I’d chosen the right path for my publication. And unfortunately, facing people like this guy is sometimes just part of that journey.