Best way to describe Piccolo and Kami were they were two halts of a whole. Nail was a separate entity who merged with Piccolo. Kami also merged with him as they didn't fuse into their original being which was because Picccolo refused to do so, as Kami and King Piccolo were a separate individual, not the two they were when they were sent it earth.
The piccolo we all know from Z was a fighter type, the only Namekian of that type in existence besides Slug. Nail was a warrior type, the last on Namek as the others ones were killed by Fireza, Dadoria, and so on. Kami and Dende are dragon clan types which is why they can make dragon balls, King Piccolo was also one thus the black star balls in GT.
So when he merged with Nail and Kami both he became the Super Namek as he became all three types of Namekians, or the ultimate Namek for lack of a better term. Tough Kami did mellow him out as dragon types are peaceful like Kami and Dende