There’s a lot you can hide with outsourced software engineering. With animation it’s all on display.
But anyway studios have been outsourcing animation work to Asian countries for a while now.
You might have seen some of the work product from one of the larger Japanese animation studios: TMS Enterainment who has worked on things like Batman: The Animated Series, Batman Beyond, The New Batman Adventures in addition to shows like Tiny Toon Adventures and Transformers in the 80-90s.
Some more recent(ish) examples are Cartoon Network outsourcing the animation for Steven Universe to Rough Draft Korea located South Korea and Nickelodeon outsourced some of the work for Korra to a Japanese company called Pierrot.
I'm just rambling at this point so I'm going to just leave a few links below that can do a better job of illustrating than I'm able to.
Wikipedia, Outsourcing of Animation: https://en.wikipedia.org/wiki/Outsourcing_of_animation
[DCAU Fandom Wiki, TMS Entertainment: https://dcau.fandom.com/wiki/TMS_Entertainment,_Ltd.
Reddit thread, Stylistic differences between two studios: https://www.reddit.com/r/TheLastAirbender/comments/1m4wbn/st...
AnimeNewsNetwork, American animation outsourced to Japan (2015): https://www.animenewsnetwork.com/answerman/2015-11-02/.94920
https://www.awn.com/animationworld/tom-jerry-produced-prague
https://www.today.com/popculture/simpsons-rides-seoul-train-...
That said, companies frequently misstep determining where they can safely outsource and where they must keep things integrated.
But for studios where mastery of a certain animation style is critical to their work, vertical integration makes sense too.
Consider that most game development studios outsource most development on a per-project basis.
Consider that most car manufacturers outsource most of their parts manufacturing to other manufacturers.
Basically: It's more unusual for a business to not be outsourcing their line of business.
It may be useful to see how others linked to this news - the original place I found this was at Engadget, which had this title: "Some Amazon and Max cartoons may have been partially animated in North Korea" https://www.engadget.com/some-amazon-and-max-cartoons-may-ha...
Which linked to Reuters: "North Koreans may have helped create Western cartoons, report says" : https://www.reuters.com/world/asia-pacific/north-koreans-may...
I linked the original report, which makes no mention of animation, but is the obvious focus of the article. The point isn't who did the outsourcing, but what was done, IMO.
The length limit on HN titles sometimes makes nuance difficult - maybe I should have added "may have been outsourced" instead. I was not going for clickbait/misrepresentation.