There is certainly more to this than what the author is saying. IIRC the explanation has to do with the difference in how you would experience the passage of time when traveling at near lightspeed as compared to a stationary frame of reference (i.e. I fire the bullet across my ship and it travels a distance X in what appears to be short time to the me the speeding guy, but to the stationary guy, a longer time passes before the bullet travels X across the ship, resulting in different speed measurements ), but I'd need to review some materials as well as being less tired and inebriated to be sure I know what I'm talking about. I'll try to remember to come back to this tomorrow