Loona is an impatient person, as well as antisocial, so I imagine that when she realized she wanted to spend more time with this couple, she immediately resorted to the one thing she knows she's good at: sex appeal.
She didn't have much time to think, and isn't particularly clever at navigating relationships, so this little moment is kind of a knee-jerk reaction for her. She doesn't realize that maybe she should just wait.