it always depends on the level of symmetry though
if he used the first design on a huge landscape and slowly morphed it to create rolling hills, technically any single section would be relatively symmetrical to the other part, but due to its scale it doesn't look bad.
just because it looks bad doesn't mean it never happens in nature; its all about the final product. this is why progress checks on terrain don't really work well.
the best way to build terrain is to plan it first. know how the hills will shape, how high the cliffs will be, how craggy the terrain will be, and how it will look on every scale before building. it takes time, but the final product is something reliably good.
