> Sushi didn’t magically come into existence across all of Japan simultaneously.

Welp. It didn't even originate in Japan specifically.

https://en.wikipedia.org/wiki/History_of_sushi

Exactly my point. Most things gradually get incorporated into a larger culture, like yoga.

If I take yoga, and call it something else without actually changing the fundamentals and say it is superior, that’s appropriation.

Nope, it’s called appropriation even if you credit the original culture and keep the same name: https://en.wikipedia.org/wiki/Cultural_appropriation

A restaurant was protested for cultural appropriation because the owner was white and it was serving Sonoran recipes under the original name. It was just the fact that a white person was profiting off of that particular subculture that made it appropriation.