I think he means that conceptually, the greater your ego and 'belief in yourself', the more charm and charisma you will be able to pull off. In an RP sense rather than mechanical.

Obviously if you get a % boost to your ego value in the game, you don't get more charisma stat.

But if you get a % boost to your mana value, you don't get more intelligence stat. (That'd be pretty sweet if you did though.)