It's worth mentioning that this is likely measuring people who identify as mixed race, especially if the data is pulled from places like federal censuses. There are plenty of people I know in the US who are mixed but don't identify as such: Barack Obama being a famous example, some of my cousins on a more personal example. There's also plenty of people who identify that they are mixed race based on family legends that may not be based in genetics/biology-
there are a million posts all over genealogy forums in the past few years of people expecting to have some Native American results in their DNA results but come up 100% European.
Also worth noting, that some mixed race people may not be counted by censuses- in some cases the census doesn't provide an option for them to choose mixed ancestry. Or they might not be citizens of the country in which they reside, while the country of their citizenship might not count overseas citizens in their census.