Now, with all that said, I'm sure that labels, individual perception and cultural factors all play into this.....I know some guys from other cultures are much more 'free' about being close to other guys and behavior we'd consider 'crossing the line' is more normal there.
Okay, to be serious: Your point about cultural differences is precisely, exactly, nail-on-the-head why there end up being deep (and often heated) conversations on the internet about what makes something gay. "Gay" is not a thing in the real world. People of the same gender falling in love with (or fucking, or wanting to fuck or fall in love with) people of the same gender? That's totally normal and natural. It's a thing in the real world. Ideas like "gay" or "queer" or "straight" are things we've invented. They exist - like culture - entirely in our heads, but we play them out in the real world. These ideas are just simulacra - images of the natural order coloured and shaped by culture.
I can tell you from experience that being gay in Toronto is very different from being gay in any place in the US where I (or my friends) have been. Further, being gay and from a WASPy background in Toronto is very different than being gay and being from a French Canadian background in Toronto. Or any other background, for that matter. And being gay and under 50 is very different from being gay and over 50. Hell, what makes something "gay" can change from one set of friends to another.
My friends and I - straight, queer, male, female, and trans alike - hug. We just do. It's rude not to. But I've seen people on this very forum swear up and down that only homos and women hug. Someone I know spends much of his time in skimpy shorts and in full body contact with other men. But because he's a fighter it's not gay. One of my friends comes from an area of Pakistan where he says it's weird for men not to hold hands. In Toronto, men who hold hands do a lot more than that when they get home. A friend of mine is hetero - kids, wife, and all - and fucking loves musicals. I can't stand them...but I love the cock.
When something crosses the line between gay and straight is almost entirely culturally-bound - and even within one culture (as if it's even possible for a single culture to exist like an island, without any interaction with myriad other cultures) the rules are fraught with exceptions to the rule, the lines to be crossed are sometimes sharp and sometimes blurred to almost invisibility.
So it's a hard question you answered - quite possibly an impossible question to answer - because there are as many answers as there are people.