[There are a few reasons that he clues in just then- because not only has Naruto spoken with her a few times himself, but he's also met another person that knew her and- told him she was too old for him... actually. Naruto's laugh is a little sheepish. It isn't a stretch to imagine what she must be thinking, and he called Sakura-chan a friend so easily. People probably think it's weird.]

She an' Sasuke are my teammates'ttebayo. Although they're a lot older than I remember them from back home. Where I'm from we're all still the same age, and we're fighting in a war together.

[It's surprisingly easy to mention it, despite their dire situation. All he can do is believe that they'll work hard enough to overcome their obstacles- and if it's team seven together, then he has no reason to believe they'll fail. The timid edge leaves his smile only to be replaced, inch by inch, by genuine tenderness.]

She's somethin' else, huh?