Although only KSC exists on the planet so far in the game's unfinished state, they would have to have metal mines to make rocket parts, roads to transport materials to KSC, farms to feed themselves, etc. One can and must assume a whole world full of industry and infrastructure existed and created KSC. So when you get wheels in the game, this is not the first wheel ever invented on the Kerbal planet. It's the first wheel designed for use on space vehicles.