The story isn't about them being gay. Its about them being in love and dealing with the post apocalyptic bullshit along with their relationship. To call it a "gay story" is to single out the one tiny part of it that is them being gay and reduce the whole thing to that. I doubt you'd just classify Schindlers list as a "Jew story" or Black panther as a "Black story". I do like how you slipped from it being a "gay story" to a "gay love story" tho, nice save. The quote was about people calling it a gay story, not a gay love story. I think even subconsciously you understand that "gay story" is not really a good way to summarize that story.
In no world is somebody asking for more detail on a story going to want to hear "its a gay story" and be satisfied. If they want details you'd tell them more, and if they didn't a more accurate summary would be "love story" or even "post apocalyptic gay love story" but just "gay story" is like calling lord of the rings a "travel diary"
By who? Unless you're clicking tags on netflix I don't think anyone is going to have this hypothetical convo:
Oh there's a great episode you should watch
Oh whats it about? Tell me more?
Its gay
Oh ok thanks, all I need to know.
The quote is about them calling it a "gay story" not a "post apocalyptic gay love story". The reductive 2 word description is rightfully annoying to a man who brought a well written and fleshed out love story to life, only to be told he made a "gay story"