I think what confuses people is that he 1) claims that morality isn't arbitrary and we can make definitive statements about it 2) Also claims no universally compelling arguments.

How does this differ from gustatory preferences?

1a) My preference for vanilla over chocolate ice cream is not arbitrary -- I really do have that preference, and I can't will myself to have a different one, and there are specific physical causes for my preference being what it is. To call the preference 'arbitrary' is like calling gravitation or pencils 'arbitrary', and carries no sting.

1b) My preference is physically instantiated, and we can make definitive statements about it, as about any other natural phenomenon.

2) There is no argument that could force any and all possible minds to like vanilla ice cream.

I raise the analogy because it seems an obvious one to me, so I don't see where the confusion is. Eliezer views ethics the same way just about everyone intuitively view aesthetics -- as a body of facts that can be empirically studied and are not purely a matter of personal opinion or ad-hoc stipulation -- facts, though, that make ineliminable reference to the neurally encoded preferences of specific organisms, facts that are not written in the sky and do not possess a value causally independent of the minds in question.

It's an entirely semantic confusion.

I don't know what you mean by this. Obviously semantics matters for disentangling moral confusions. But the facts I outlined above about how ice cream preference works are not linguistic facts.