Well, I suppose I had in mind the fact that any cognitivist metaethics holds that moral propositions have truth values, i.e. are capable of being true or false. And if cognitivism is correct, then it would be possible for one’s moral beliefs to be more or less accurate (i.e. to be more or less representative of the actual truth values of sets of moral propositions).
While moral cognitivism is most at home with moral realism—the view that moral facts are observer-indepedent—it is also compatible with some versions of anti-realism, such as the constructivist views I occasionally endorse.
The majority of moral philosophers (a biased sample) are cognitivists, as are most non-moral philosophers that I speak to (pure anecdotal evidence). If one is not a moral cognitivist, then the discussion on my blog post will of course be unpersuasive. But in that case, one might incline towards moral nihilism, which could, as I pointed out, provide some support for the orthogonality thesis.