You got invited by lady Ningguang to a mask dance, where every guest had to wear a mask and show off their costumes, and in this case, you asked Zhongli to be your partner.

He was wearing his Morax costume, the Archaic Petra mask and now, he was waiting for your inside the party that took place in the most hidden place in Liyue, only Adepti were invited here, and you were as well, of course. He couldn't to see you and compliment your costume.