That much was obvious. When you build your examples around a sexist experience of sexist media, your examples will themselves end up sexist. I mean, why isn't Zoe buying, too? What is it that Inara's selling? I think we know, and from the heternormative misogyny rises the situation in which a cheeky description of market making has exclusively men buying and exclusively women selling.
For the record, I made no connection between Inara's occupation on the show, and her "selling" in this example. I doubt Chris intended such a connection.