I know I'll get all kinds of shit for saying this but...this guy doesn't look gay. And yes, there is a look, there are mannerisms; there is a feeling you get when you look at someone (particularly when you make eye contact) that he, too, is gay (whether you are interested or not, it's an unspoken acknowledgement). I have seen many, many, many gay men and women since I came out at 15, and can tell pretty fast. This guy isn't.
What I experienced very early (came out at 15, started sneaking into clubs at 17) is rare: I listened with interest to older gay men. I knew at the time that older gay men knew what they were talking about, and I took their advice. (this was 1990-something; I was told I would likely die of either AIDS or suicide...I believed this and desperately wanted to learn as much as possible to not end up like that). I knew that a lot of not-gay guys would hang out at the bars because gay men are very easy targets for robbery, they tend to overdo it when dressing up to go out; the same way that a woman can 'advertise' her body and give men the wrong idea, gay men do this and imply they're rich when they really aren't - they just want you to think they're wearing $600 jeans. Unfortunately, criminals who can and will strong-arm us don't know that - they are either so messed up from heroin or meth or coke that they'll do anything to get money for their next fix. A lot of them know that if they hit the gay clubs on busy nights, typically nights when the cops are having an equally busy night dealing with fights, fires, accidents, etc., these guys know that if you call 911 nobody's coming for at least 45 minutes. The criminal can be halfway to another state by that time. I've seen this happen twice to a friend in Minneapolis, he is latino and there's this stereotype among a lot of these black kids downtown that 'the latins don't speak English; they're here illegally and they won't go to the cops' - he's been robbed twice because of this, despite my pleading with him to call a cab or please don't walk home alone.
The thing in the gay world is that about 85% of us have no interest or attraction when it comes to other gay men; we desperately want to get our hands on what we can't have (the straight college athlete with a rugby player's body). Thing is, most of those guys, not only aren't gay, but if they are, they don't go to these clubs. Most are pretty repressed and hang out in online chats. Pretty much the crowd you see at the gay clubs in one city is the same as any other city, just with different accents and slightly friendly/less friendly attitudes.