Grandmaster of demonic cultivation, 2

On Mount Brahma, Wei Wuxian improvises a flute and begins to play. Something powerfully catches Lan Wangji's attention. What has he noticed? And why is he taking Wei Wuxian to his clan residence in Gusu?. Lan Wangji is so unrecognizable that he seems different: he hides alcohol in his room, tolerates Wei Wuxian's antics... and even lets him spend the night on top of him! It's hard to believe that he's the same Lan Zhan who used to keep his distance from everyone.