Will be interesting when/if the full video releases, this one's been cut and edited as it looks to jump around. It looks like Conor actually has his hand in the air doing a fist pump, as if he's cheering or chanting or something. The drink you see in the hand looks to be in the hand of the guy in the white shirt further down the bar, kind of an optical illusion, and he looks to cheering or toasting or whatever with Conor. Conor doesn't take a drink, he moves his empty hand by his mouth, it looks more like he's scratching his beard. Then he lunges into a sucker punch into the guys cheek area.
I'm watching this in slow on a second monitor which is why this sounds like play-by-play lol.
But yeah, he didn't throw a drink at him from the looks of it, he punched him. In fact, looking again, it looks like the glass Conor poured the drink into in front of him hasn't even moved at all from the bar.