Not quite as much of a coincidence as you might think. Many of these algorithms come from graphics researchers presenting at SIGGRAPH (https://www.siggraph.org, the leading conference).

So if so if Jet Set Radio was released June 2000, you can look for related papers a couple years before to see if new techniques were appearing. And, in fact, they were!

Disney paper (1998) on texture mapping for cell shading (the color of a cartoon):

https://media.disneyanimation.com/uploads/production/publica...

NYU paper (1998) applying outlines to 3d objects (the black outline of a cartoon) :

https://mrl.cs.nyu.edu/publications/npr-course1999/hertzmann...