But importantly, when Eliezer says something is "good" he doesn't mean quite the same thing I mean when I say something is "good." We actually speak slightly different languages in which the word "good" has slightly different meaning

In http://lesswrong.com/lw/t0/abstracted_idealized_dynamics/mgr, user steven wrote "When X (an agent) judges that Y (another agent) should Z (take some action, make some decision), X is judging that Z is the solution to the problem W (perhaps increasing a world's measure under some optimization criterion), where W is a rigid designator for the problem structure implicitly defined by the machinery shared by X and Y which they both use to make desirability judgments. (Or at least X is asserting that it's shared.) Due to the nature of W, becoming informed will cause X and Y to get closer to the solution of W, but wanting-it-when-informed is not what makes that solution moral." with which Eliezer agreed.

This means that, even though people might presently have different things in mind when they say something is "good", Eliezer does not regard their/our/his present ideas as either the meaning of their-form-of-good or his-form-of-good. The meaning of good is not "the things someone/anyone personally, presently finds morally compelling", but something like "the fixed facts that are found but not defined by clarifying the result of applying the shared human evaluative cognitive machinery to a wide variety of situations under reflectively ideal conditions of information." That is to say, Eliezer thinks, not only that moral questions are well defined, "objective", in a realist or cognitivist way, but that our present explicit-moralities all have a single, fixed, external referent which is constructively revealed via the moral computations that weigh our many criteria.

I haven't finished reading CEV, but here's a quote from Levels of Organization that seems relevant: "The target matter of Artificial Intelligence is not the surface variation that makes one human slightly smarter than another human, but rather the vast store of complexity that separates a human from an amoeba". Similarly, the target matter of inferences that figure out the content of morality is not the surface variation of moral intuitions and beliefs under partial information which result in moral disagreements, but the vast store of neural complexity that allows humans to disagree at all, rather than merely be asking different questions.

So the meaning of presently-acted-upon-and-explicitly-stated-rightness in your language, and the meaning of it in my language might be different, but one of the many points of the meta-ethics sequence is that the expanded-enlightened-mature-unfolding of those present usages gives us a single, shared, expanded-meaning in both our languages.

If you still think that moral relativism is a good way to convey that in daily language, fine. It seems the most charitable way in which he could be interpreted as a relativist is if "good" is always in quotes, to denote the present meaning a person attaches to the word. He is a "moral" relativist, and a moral realist/cognitivist/constructivist.