'rigs' are often lighter and extend further away from the car than video
or cine rigs or car mounts as photographic cameras are much lighter than
most video and cine equipment.
There are many, many different ways to mount a camera to a car and there is no single perfect 'rig' or 'car mount'. The desired image, conditions, photographic or video equipment, car and many other factors will all determine which rig or car mount will be needed to achieve the desired goal.
For the sake of clarification anything which allows you to attach a photographic device to a car can be considered to be a 'rig' or 'car mount'.