Claudius laughs, and though it's hardly traditional to toast with tea, he does so now. "And I've witnessed the exemplary and diligent disciple you once were, not to mention the fine cultivator you've become." The formality is teasing, in a way it wouldn't have been before. Lan Wangji may or may not catch the nuances, but the intent is there. "At least thou gav'st him leave to explain himself, however inexplicably. I'm quite grateful he's here."