He really knows her. He’s the one who hunted her down in her past life and ended up as a one-night stand. It looks like you didn’t read much, it’s already mentioned in previous chapters what happened to the real Cheng (blond guy), and the butler notices that his master has become a different person. Is my translation that confusing? Chuchu doesn’t know that he’s also a transmigrator.
I wonder if the person Chuchu is chatting with is the blond guy. I’m guessing it’s Bobo (new character). It’s confusing because he’s also tracking Chuchu, so maybe he is the subordinate Chuchu talking to.