It's a combination of things.
Women are a lot better at picking up on nonverbal cues. They sense when a man is confident, when he doesn't "give a fuck" when he's taken and women are turned on by that. They get intrigued. A woman's mindset is always "that guy is worth something" if they see one of those indicators.
Of course you can always be a high caliber fuckboy and fake all those things just because you're a decent looking guy and slightly arrogant. But another way, an effective way, of faking it unintentionally is by having a girl you're fucking, or dating, or whatever. You naturally are content with yourself, or with the 'night' because hey you have pussy waiting for you, right?
It's all a game that you're willingly or unwillingly in. So, whenever someone tells you that it's immature to say "it's a game" tell them to fuck off. Honestly, life is a goddamn game and some people play it better than others.