Regardless of what specific term is used, it is used (and abused!) equivalently pretty much everywhere humans exist.
Is ‘caste’, race? Because it sure is used that way (or worse) in places that have it. And that’s been going on for longer than what we currently call European civilization.
Caste is synonymous with social class. There is no genetic or racial component to it, and no one is claiming as such (including the people who are discriminating on the basis of caste).
The study shows the reverse effect. Because of the emergence of the caste system and rigid classes people stopped intermixing across caste boundaries and now 2000 years later you can find certain genetic differentiators between them.
The reality is the same for "Race" and "Ethnicity", and all sorts of other words that humans have used to categorize "not my family".
French colonists to the new world freely intermarried (and had kids) with Native Americans and people brought over from Africa, and eventually those same groups were prevented from marrying under racist american laws.
So there's lots of french blood in black people in the southern united states, but they were eventually prevented from marrying white french people, even when they were literally part of the same large family tree! There are long lines and families of black people who literally descend from my ancestors that I wouldn't have been allowed to marry!
Which should clearly demonstrate that it was never about your genetic or biologic ancestry, as modern science knows.
Wikipedia claims America's "blacks can't marry whites" laws have no precedent.
Similarly, there was lots of inter-racial relations before some colonies banned it, and other colonies never banned it.
Is ‘caste’, race? Because it sure is used that way (or worse) in places that have it. And that’s been going on for longer than what we currently call European civilization.