As always, Michael takes for granted the fact that Lee wouldn't lie to him. If she wanted to stay more than she wanted to go back to his place and do it, she'd say so. Just like she'd told him she was going to keep on drinking a minute ago, thank him very much. Even when he doesn't agree with her, he finds her bossy side reassuring.
Michael leans forward to kiss her, because he can do that here with everyone around and they don't have to worry about it. It's clumsy; he almost spills the remainder of his drink, although he doesn't notice.
“Cab?” he asks. It's probably the safest option at the moment.