He was begging for the notebook to be stolen by leaving it behind and not even trying to keep it secret and secure. Filthy thieves are everywhere, after all. Nasty hobbitses. Let's hope he learns something from his mistakes, though I'm not expecting much. After all, he's the reincarnation of a member of a royal family that couldn't protect itself. That tells something about them.
Actually, couldn't he use magic to find it once he notices? Seems like a pretty simple thing considering it was his personal property.