(He has other cast iron videos as well)
Cast iron season right is as non-stick as any of the newer non-stick surfaces.
It's been my experiences, that the factory coating will not last long and very quickly the taste and smell of cast iron will leach into the prepared food you just cooked in it. Especially true in cornbread.
There are a dozen different ways to properly season cast iron, but rather than type them out again, just watch the video.
Regarding 'black bits' coming off. That usually means oils and fats have been excessively built up and burned on, normally where the sides meet the bottom on the inside of the skillet/pan, and on the exterior bottom where the ridge is and it needs to come off.