From what I can tell, they are not using 3D objects. They are also not animating between 400 images of a car at a different angle. They’re doing a mix of rotating image assets and animating between ~50-70 images of a car at different angles. The illusion is perfect because it really does look like they used 3D car models !
Look at this GIF of a Uber car turning a corner (Dropbox link):
We can clearly see that that the shadow and the car’s view angle doesn’t update as often as the car’s rotation.
Here I overlaid 2 images of the car at different angles, but using the same car image:
We can see that the map is rotated ~5 degrees but the car image is perfectly clear because it hasn’t changed, it was simply rotated.