I still do not understand why this "official" extra text from Emet's perspective goes against how he describes the Sundering within the game, where he demonstrates it as perfectly splitting a person into two copies with no mention of the horror of seeing them reduced to literal malformed creatures.

When there's a mismatch between actual canon and a simplified summary written for the audience of another game (and in this case until and unless we get a better explanation from the creators), I'm going to assume the discrepancy is down to the external version taking creative liberties for the sake of a self-contained capsule of story.