I don't think you're "confused" about what was meant. I think you understood exactly what was meant, and have identified a real (and, I believe, acknowledged?) problem with the moral realist definition of Good.

The assumption is that "if we knew more, thought faster, were more the people we wished we were, had grown up farther together” then a very large number of humans would converge onto moral agreement.

It's not the assumption that is good or bad, but the quality of argument provided for it.