CarPlay devices (car components) are essentially playing a streaming video of a hidden display generated by the phone. CarPlay also lets those devices send back touch events to trigger buttons and other interactions. Very little process is done on the vehicle.

BTW if you are plugged in to CarPlay and take a screen shot, it will include the hidden CarPlay screen.

CarPlay is rendered by the phone itself, so it's not strictly a function of how powerful the car infotainment is. You've been able to talk to Siri since the beginning of CarPlay so additional voice control is really just an accessibility thing

Some cars already have a voice control button on the wheel for their existing system which, if done correctly, is overriden by Siri+CarPlay. Which is really nice when it works.

I’m able to control carplay by just saying “Hey Siri.” Siri’s abilities tend to fluctuate based on what Apple is doing on the server, the phase of the moon and whether I remembered to sacrifice a chicken that morning, but otherwise, it seems to work fine.