> I could also speculate that the overlap between Linux kernel developers and automotive and industrial embedded systems is pretty low.

Agreed.

> So the high bug severity in the CAN driver could be developers contributing patches from a very different programming background?

Background and situation. Their mindset is "I need this to work, right now", not "I need this to work, and not break anything else, forever".

There are so many more embedded CAN systems beyond cars. Industrial battery management uses Linux and canbus, for example.