Reposting part of a comment I made in another thread about this, but:

animation across east Asian countries outsources labor between each other all of the time. Your Japanese anime is just as much Korean, Chinese, and Vietnamese at this point, as it is Japanese.

Go look at the credits of most modern anime productions out of Japan, and large swathes of the names you see aren't Japanese, but are from those other countries.

Even a fairly low stakes, low budget, slice of life anime, like Non Non Biyori has Vietnamese names all over its god damn credits, because globalization has impacted the east Asian animation industry in such a way, that there's an large cross pollination of talent across borders, for better and worse.

And that's not to mention the western animation that gets outsourced to these places, South Korea especially.

The fact North Korea is also involved in this complex outsourcing process shouldn't be surprising to anyone who knows anything about how that industry works.