Coast also has greater food production than Oceans.
My guess is that he was suggesting a spell that "raises" or "lowers" land, which would mean: Ocean<->Coast<->Plains<->Hills<->Mountains
Civ IV doesn't have any pre-programmed notion of land height, but I don't see why this would be difficult to implement. Perhaps it would be better balanced to implement terraforming as a mix of spells: Water spells to create water tiles, Earth spells to create mountainous terrain, etc.