I'm no moral philosopher, but it seems that the difference is between claiming or not claiming that the 'moral judger' is a thing that actually exists. See divine command theory vs. ideal observer theory.

Once more, I'm no decision theorist, and I barely know a thing about AI, let alone corrigibility, but the author doesn't seem to be making a metaethical argument so much as a decision-theoretic one (?), so I don't see the relevance of your question.