>>150393375
Netflix financed the movie and own the IP rights after Sony rejected financing it themselves, but Netflix had a contract with Sony Pictures Animation where Sony had to animate the film.
Sony Pictures Animation, the studio that animated it, is American.
https://en.wikipedia.org/wiki/Sony_Pictures_Animation
Then there's Korean people on the staff of Sony Pictures Animation that came up with the concepts and writing and songs.
It's not an entirely Korean production since Sony Pictures Animation made it, but it definitely has a Korean connection through the staff and director