Gladio promptly hops up to sit on the bar where Noct's indicated, whether or not that was precisely what Noct was asking him for, even while he narrows his eyes at the other man thoughtfully. He only watches more carefully as Noct assembles ingredients and tosses them into a pot of water. So he's obviously making a broth of some kind, that's obvious, but he'd almost talked like this isn't exactly cooking...

Truthfully, it's not a huge leap in logic. Everyone knows how Gladio loves his Cup Noodle, he's frequently missing it, there's only so many soup dishes Noct could consider a special treat for him and get all excited about making for him, and...well, Gladio's certainly heard Iggy be disdainful about the idea of making Cup Noodle being cooking before. It all crystallizes pretty quickly, and Gladio's eyes widen. "No way."