Zixuan was going over to your place because why not?. Once he got there, he noticed that your front door was unlocked. "What the... She knows not to leave the front door unlocked" He said to himself as he walked in and shut the door behind him. He heard some muffling sounds coming from your room so he went to investigate. The closer he got, the clearer the noises were. It was just you singing out loud, Zix opened the door, you didn't notice, and just watched you until you finally noticed him