Do you have some insight about why this reversal might have occurred?
This is a semantic issue. Ethnic groups are constructs. A system which misidentifies people identifies all people poorly.
It doesn’t track across regions either. People labelled “white” by law in some countries (Brazil, South Africa, etc) would be classified as “black” elsewhere.
In England, the example here, we do not classify people the way the Us does, with its history of “one drop” politics. Many British people considered “white” are “black” in the US.
There is no scientifically valid way of defining who counts as “black” so any discussion of tuning a system based on this definition is a disaster.
Even the people commenting are talking about different groups based on their own culture and prejudices.
I'm also British, can you give an example of that? A minor celebrity/TV personality say?
To the extent you have a point though I think it's irrelevant anyway—they paused the programme because they found, according to whatever definition they measured with, it had that skew.