"If you want to make an apple pie from scratch, you must first create the universe." ~ Dr. Carl Sagan. Is he using an existing processor / memory / motherboard? Is he using an operating system? Is he using a compiler, editor, IDE? Is he using a standard library? Is he using any 3rd party libraries? Just because he isn't using an engine doesn't mean it's made "from scratch".
[1] http://www.cl.cam.ac.uk/projects/raspberrypi/tutorials/os/