On a near-noise level, virtually all conversation or interaction can and mostly does contain shades of meaning expressing things that when verbalized explicitly would be considered rude or inappropriate. From that POV, the term appears meaningless or redundant. Otherwise we'd communicate like Vulcans.

EDIT: I find it also peculiar that the explanation you've cited only mentions "racial slights", despite neither "micro-" nor "-aggression" containing this meaning. But it's comforting to know that one is at least safe from committing such things across all the other social boundaries! /s