The timing doesn't line up. BYD has already been selling EVs by the time Tesla opened a factory in China. Heck, they were selling EVs even before _Tesla_ existed.

And they clearly have their own expertise. There are videos of BYD and Tesla car teardowns, and you can see that they quite differ in design philosophies.

I think China was more interested in creating more competition internally, rather than just ripping off the technology.