They did not assume it was only for bored boyfriends. They thanked the person who thought about bored boyfriends. That means the chairs are at least partly for bored boyfriends but not exclusively for bored boyfriends. The person replying, if a boyfriend, would have a convoluted thought process if it was 'I'm glad the person who designed the space thought about other people than me that I can also obviously make use of' rather than 'I'm glad the people who designed the space thought about me' when seeing something that benefits them directly.
> homosexual erasure
I feel your assumption that a bored boyfriend being considered is homosexual erasure ignores the boyfriends of other men. Or perhaps you meant something more specific but didn't specify? Perhaps you'd like myself and others to check before jumping to a conclusion about your motives rather than calling you a homophobe? Why not extend us the same courtesy.