You really can't fault Setsurou for looking surprised.
Mostly because he doesn't.
Also, an angel appears to playing patty-cake with Momoka's taste buds right now. That's how good it is.
"My cuisine is sour-proof." He states simply. "And you've always been a woman of utilitarian tastes. I say we speak of it now where the food can diminish the impact of any potential unpleasantness. And then we can move on to more delightful things. I imagine you do not plan to get back to work immediately after dinner."
"A Captain, huh? And who's she fightin'? I didn't hear any alarms. The way this is set up it sounds more like a party."