I don't understand whats flamebaity about the OP. This is an article literally about skin colors; thus it is somewhat natural that the word "racism" will appear in a harmless way, as here.

It wasn't in a harmless way; it was making an inflammatory accusation of racism; not only that, but in a form which is repeated so often as to be a flamewar trope ("that's racist"), and in a way that clearly signalled ideological battle. That is exactly the sort of thing the HN guidelines ask commenters to avoid.