Crikey, I'd never heard about that story. Blimey, who the hell says shit like that?
It weirdly explains a lot though. I've had a few problems with the accusations that Britain is racist to Markle, largely because it seems to ignore the reality that the working class of my generation (Gen X) saw a fairly high number of mixed race children born to one English parent and one West Indian parent, and many of those parents freely married in Britain in the 60s and 70s when there were fairly severe civil rights problems in the US.
To say Britain is racist, to me, is to deny that British society and culture is full of mixed race middle-aged people now in their own mixed marriages who are an integral part of British life and society, and have been for decades.
The Markle racism angle almost seems to suggest that she is the only mixed race woman ever to set foot in Britain. 
But weirdly, I'm wondering if a lot of this is because Harry has lived in a bubble world where Markle is the first biracial woman ever to enter the fold in a real way. And he assumes Britain is like the world he has lived in (where exposure to people of colour has been limited), whereas, in reality, many ordinary white people have had biracial children and adults in their families and lives for up to fifty years or so now.