What does Mrs. Murrow suspect is the reason for Holden's going home late on a Saturday night?

Mrs. Murrow asks Holden if he is going home because someone in his family is sick. Holden lies and says that he has to go home because he is having an operation. She is so sympathetic that Holden begins to feel guilty for the lies he has told. Since Holden lies to her, seemingly just for fun, we, as the reader, have to question how much truth he, as the narrator, tells us.