These open source elements have be integrated into their UI so at least their UI should be GPL too. The letter indicates that they have only provided the source for what they included and not the derivatives which must also be GPL'd.
There may well be further proprietary source from the car that they don't need to include but anything that incorporates opensource components takes on the opensource licence and must be provided, it does not appear they have done that.
Biting the hand that feeds IT
