The moment he realizes it isn't Kano, Shintaro's shoulders relax just a bit. When it isn't Kido, he realizes that this guest must not be here for him or Momo. There was a chance it was Momo, but he has a feeling that if Momo had friends here, she would first want them to call her before visiting just to have that experience of discussing plans over a phone. And that is how Shintaro concludes even before Shinji asks that this unfamiliar kid standing before him must be a guest for their third roommate.

"Nagisa-san? Yeah, he lives here, but he's out right now. He's not usually here."