That was something different of Lisa's usual manner, don't you think? Does she now taking a delight from jeering at her brother and his good-for-nothing friend?
Actually, while it differs from the way Lisa has been written in recent years, it's much closer to her character in the early seasons of the show. I think it's a positive move on the part of the writers as Lisa's character (among others...) from the Scully era onwards, has been lacking in the depth and realism that she used to have.