That book relies on a wrong model for the speed of light. The author argues that you can assume that the speed of a source of light is added to the motion of light itself, increasing its speed. This flies in the face of evidence accumulated since the Michelson-Morley Experiments in the late 1880s, that demonstrated that the speed of light is independent of the motion of the source. All observers measure the speed of light to be the same, constant value, regardless of relative velocity. This is why you should be very careful about content lying around on the internet - you never know who wrote it or whether or not they understand basic observations about the universe around us. I hope this helps you be a bit more careful about choosing sources.