I don't think the book is saying the car is uniform. It is a little confusing - at least from the little bit I can see.
The sphere is uniform.
Uniform shaped solids would be things like a sphere, a circular object, a square, a rectangle.
The C of M with a uniform object like those is then where you would expect.
Uniform also means that the object has uniform density. That is certainly not the case for the car.
It does though, beg the question of where the 'centre of an object' is.
For example, the C of M of a ring or hoop is at the centre of the circle. So it isn't within a physical part of the object.
You see this with that horse shoe in the 3rd object.
The centre of mass of a triangle is, well, at the centre of the triangle. But where is that?
This can actually be determined by a bit of geometry.