At Magnus' voice on his title, Lan Wangji does look up. Context makes it reasonably obvious what they mean. He has seen Shen Yuan sitting on this couch, playing this game, before. He hesitates. "This is Shen Yuan's game." What he means by that is that Shen Yuan does not like him whatsoever. Although the feeling is mutual, it might be disrespectful to the dead to allow a man he hates to toy with his belongings.