Gotta admit that was cathartic to some extent. Best boy.
If you remember, she said that she couldn't get with him because she say him as a little brother or was too connected to him. But now that she sees him as a stranger...
@Stephanieisanerd It's a little weird out of context, sure, but knowing these two characters and how much of a tsundere she is, it makes the situation more understandable.
It was just a kiss, and it's not like he did anything else, and she's the type that won't admit her feelings.