Wait, the 2 of them literally just walk inside Together. She more or less watched the entire thing. Her sister could have met him before, went out for food, then brought him back. But then their conversation would be very different than what it was. They both were willing to call the police, and both expected a burgler to be in the house. If he was a burgler, why would he be so willing to call the police, and if so, then wtf is wrong with Japan's burgler population being so high an appartment gets double-hit in the same afternoon?
How the fuck could that explination possibly work? There is a limit to being stupid where you forget what you literally just watched because someone told you otherwise.