"Huh, really?" It's not unheard of back home, certainly, but it's unusual. An orphan would typically be adopted quickly, or at least looked after to the point it was an adoption in all but name. He thinks of Undyne and then pulls away from that thought like it's on fire. They're all dead, it doesn't matter. Being disappointed he didn't get a startled reaction out of John is easier. (It's also noteworthy in its own way. Is he naturally calm, or is he holding his reactions in check on purpose?) "Well, I'm sure Papyrus'll be thrilled to add you to the family. Do some father son bonding. Playing catch or something."

Though John looks a little old for that. He's gotten better at determining human age since he came to Sweetwater, and John doesn't exactly look like a little kid. Probably a teenager.