Every homogeneous country takes pride in their culture and food as an aspect of culture. While most countries promote pride in culture and nationality, the US and a handful of other countries actively play down promoting pride in those things. If you say "American culture" and "national pride" they somehow have a negative connotation. Since food is a part of culture, Americans taking pride in food feels off somehow. There's also the fact that a lot of American foods are bastardized/corporatized versions of some other country's food. I think apple pie and tater tots are American in origin, and maybe at some point in history people took pride in that, but not anymore. We're like, it's just apple pie and tater tots. So since the manga is written for a Japanese audience it actually appeals to their readers that someone in a lower social position would become "cultured" by enjoying Japanese food, and if the person is actually in a high social position then even better. Honestly I don't know how to feel about all that. The first time I saw KFC and Pizza Hut in an anime my mind was screaming a dunkey "NOOOOOOOOOOOOOOOO!!!" But then I was like why wouldn't Japanese enjoy fried chicken and pizza? And speaking of pizza, that one gets strange. It feels like something American, but it originated in Italy, but then the Chinese claim it's a bastardized version of one of their old recipes Marco Polo copied so they're claiming to have originated it. But then it's like couldn't it also be possible that people all over the world who can make bread were like let's bake some non-bread items on this bread and eat it? Similarly, how unique is it to bake apple pie when apples aren't from America? Food rabbit hole is deep.