Painting a car is quite a different process from painting your home. Even the paint that is used is different. It's usually an oil-based formula, whereas house paint is a water-based, acrylic formula. To provide a nice paint job, auto body workers need to know how to properly prepare the surface, and also how to create a nice, smooth finish.
What's even more amazing is that painting is just a small part of the work that auto body professionals do. You can read more about their other work, and also about auto painting, here on this website, where we write about those very topics.