It's true that he can't divorce himself from human in a sense, but a few nitpicks.
1- In theory (although probably not in practice), Vaniver could imagine himself as another sort of hypothetically or actually possible moral being. Apes have morality, for example. You could counter with Elizier's definition of morality here, but his case for moral convergence is fairly poor. 2- Even a completely amoral being can "think about morality" in the sense of attempting to predict human actions and taking moral codes into account. 3- I know this is very pedantic, but I would contend there are possible universes in which the phrase "You can't divorce yourself from being human while thinking about morality" does not apply. An Aristotelean universe in which creatures have purposes and inherently gain satisfication from fullfilling their purpose would use an Aristotelean metaethics of purpose-fullfilment, and a Christian universe a metaethics of the Will of God- both would apply.
There seems to be a widespread impression that the metaethics sequence was not very successful as an explanation of Eliezer Yudkowsky's views. It even says so on the wiki. And frankly, I'm puzzled by this... hence the "apparently" in this post's title. When I read the metaethics sequence, it seemed to make perfect sense to me. I can think of a couple things that may have made me different from the average OB/LW reader in this regard: