The recent allegation of racism in the British royal family has been all over the news. Are people... surprised by this?

I'm trying to wrap my head around the news about possible racism in the British royal family. I (an American) am under the impression that royal families are based on bloodlines. In the old days royals would marry their cousins, and I'd assume there is still a strong implication that the British ruling family would be genetically as homogenous as possible (read: ethnically British).

To be clear, the whole premise of royal bloodlines / genetic supremacy is obviously rooted in racism (as well as classism). In the context of a former colonial empire like Great Britain, it is even more racist. What I'm having trouble putting together is why the recent allegation by Meghan Markle and Prince Harry that a member of the British royal family was concerned that their baby would be "too dark" for the British monarchy seems to have broken the internet. People seem genuinely surprised that this racist "concern" would come up in a family that is literally based on British bloodline supremacy. Virtually every news source is reporting this as a shocking revelation.

Why is this breaking the news? Am I incorrect in my conception of what a monarchy is or has the conception of monarchy changed? Or are people just starting to question the idea of bloodline supremacy? Is there another angle I'm missing?