
Let's keep the different cultures in perspective.
In China, the relationship development is nothing like it is in US. You can't expect to take things lightly and go with the flow, if it is not something both partners agreed beforehand. The default mode is to take things seriously.
His friends were just telling him how the Chinese society perceives the way he is acting. It's not their fault, it's not her fault, it's just the way things go in that side of the world.

Thought it was South Korea? And I know, I'm saying I don't get why people have that kind of thought process, not that I'm expecting a different development, this is actually what I expected to happen, though it's grating on my nerves. And that I saw the same thing in American TV shows and movies, which is weird to me though I'm used to seeing it in fiction, seeing as these past few years I've been an avid consumer of Japanese, Korean, Chinese and American fiction. I'm most familiar with my own country's way of doing things, not the US way, which is why I never expected the development to be like in the US so I can't comment on the similarities of relationship development, just on them having the same mindset of "they're such good friends, they're definitely gonna date" so long as the "they" everyone is referring to is a guy and a girl.
The audacity of that girl. She knows he's gay, liking him is fine you can't help your feelings, but questioning his orientation just because she likes him? Fuck that. And the way the others acted, like being friendly automatically means you're interested. Americans have that too, the saying girls and guys can't be just friends, here though, it's completely the same treatment of friends of both sexes. It's not weird to have sleepovers, and the better ones are even gonna buy you pads or pills. Even the casual friends aren't gonna blink an eye if your legs just so happened to be hairy.