Comey asked why Trump would ask everyone to leave the Oval Office to speak with Comey unless he was doing something improper. Yet, Trump could ask why Comey would use a third party to leak these memos if they were his property and there was nothing improper in their public release.
In fact, there was a great deal wrong with their release, and Comey likely knew it. These were documents prepared on an FBI computer addressing a highly sensitive investigation on facts that he considered material to that investigation. Indeed, he conveyed that information confidentially to his top aides and later said that he wanted the information to be given to the special counsel because it was important to the investigation.