It was a kid. That, as much as Ellie's reaction, put Joel's guard down - if only a little, enough to keep back and let her greet her friend, anyway. While still keeping one eye on her and the other on potential exits, just in case.

"Another friend, huh?" His tone of voice held a lot of things - affection, definitely, because he knew that was just Ellie's way. People liked her, she was a nice kid, obviously even he wasn't immune to her charms. Maybe a hint of disapproval, too, or at least caution - sure, making friends her own age was probably okay, but she seemed to have a lot of people she trusted. Which made Joel wary by his very nature.