In 2006, McGruder explained in an interview, “We now have a Japanese anime studio named Madhouse to help us out”, but at some point, the deal with Madhouse fell through. Instead, the Emmy Award-winning South Korean studio Moi Animation, handled the animation for season two onwards. As a result, the following seasons of the series have more detailed animation, as well as minor updates for most of the character designs.
Yes it was. The studio was Japanese.
Can you please provide the source?
According to wikipedia there was 1 uncredited Japanese studio. The other studios were South Korean.