While Nanami doesn't understand what tuna mayo means in this context, he doubles down on committing to getting better at understanding Inumaki. Perhaps not enough to get what kind of icing he means when he says that, but more than the general excitement and pride (?) he senses.

"I have never used royal icing myself, but I've seen many examples with intricate highly detailed designs," Nanami says with approval, "That's impressive work. I hope you took some photos to capture the accomplishment."