There's a moment of brief confusion there - Bucky and Natasha? - but, right, these are different people than the ones he's used to, and who knows what things are like in their world? Sam privately wonders what two assassins do on a date; it sounds kinda Mr. & Mrs. Smith to him.

"Kid?" Sam lifts his eyebrows at that. It seems too awkward for him. "I've heard plenty of war stories. Almost as many as I've heard about the mishaps of the two of you - them - growing up together."