Two people from different races can be way more similar genetically than two people from the same race. The concept of race was built over a long story of separating humanity in different ethnic groups, and then physical characteristics of some of those ethnic groups started slowing being adopted as a mean to show that those people are intrinsically different, but they are just an unimportant set of characteristics that does not convey important information from a genetic perspective, they gained social meaning through culture. The modern concept of race took form in the enlightenment, https://twitter.com/Limerick1914/status/757227361582608384, when the original western notion of which ethnic groups exists in the world was built into a racist anthropology.
That doesn't mean that "all lives matter" or we shouldn't talk about race. Race is a social construct, and as a social construct, it exists. Money is also a social construct. But, the concept of race makes no sense besides the social structure that was built on. That why different countries consider that the set of existing races is different, for instance, the only country that really considers "latino" a race is the US.
Going back to your question, the extinct humans actually had important biological differences, the different races have not.