It was Scout's turn to squint, and so he did. She knew Ian? That idea was almost laughable. As if. Now, of course, Scout knew his brother had - hahaha - a girlfriend, but he didn't know her name and had never seen her. That, however, was very likely the end of Ian's interactions with women. Ever. And neither Boo nor Scout even knew how he'd gotten so far as to actually get a girlfriend. How did he woo her? Did she have a soft-spot for people unable to laugh? Seriously.
But this, obviously, wasn't aforementioned girlfriend, so how she knew Ian was a mystery. Scout nodded at her, wondering if she'd elaborate.