They were, ARE, the same person. For Kami to be god, he had to get rid of all the evil in him, and so Piccolo was created. Next time, pay attention cause they explained that.
piccolo is Kamis evil he expelled from him, say kami/piccolo together is Ying and Yang ones evil the other is good, only the small portions of good and evil in the opposite are hidden deep down. so they have always been connected, they always will be and they were born as one . . . so . . . yeah