Short answer is GPL3 doesn’t just require source disclosure for the software delivered but also software or firmware that it requires to function.

So say a network video player under GPL2 would require release of the player source code to whoever you give a copy of the player software to you wouldn’t have to give the source code to the video server that it needs to work with because you didn’t give them a copy of the server.

GLP3 would require you to also give the server code. So if the car thing was under GLP3 they would have to give the server code and people could run their own server for it.

That’s a simple explanation. In reality it’s more complicated but that’s the gist.