He got that information from the same place GH15 gets his information. His head.
And the fact you've made good gains doing a couple sets a body-part does not go against everything science says.
Muscle contractions require ATP. There are three ways to get there. Two of them involve a lack of oxygen so they're known as Anaerobic Pathways. The first is Anaerobic Glycolytic. The second is the Creatine Phosphate system.
So muscle contractions that are explosive and short like a powerlifter deadlifting his 3rm max requires a great deal of ATP derived from the phosphate system. Creatine is a donor of Phosphate.
Creatine DOES contribute to muscle growth, and on many levels. One of which has to do with its Osmolytic effect, in other words, it makes the cell expand because of increased water intake into the cell. This sets off a chain reaction that leads to an anabolic environment.
But muscle contractions do not make Creatine. They create a higher demand for phosphate, which can be donated by creatine, but they do not in and of themselves create Creatine.