As a general rule, yes

I look biology and I remember learning that r/k species are completely separate species

r/k describes different life strategies that exist on a spectrum (r = less offspring, more investment, k = more offspring, less investment). The r/k comparison can be made between any two populations, even individuals. They dont have to be separate species. But obviously some species are more k or more r depending on what species you are comparing them to

In the context of human race, the argument goes blacks are on one end of the spectrum and east asians on the other, with europeans falling somewhere middle. r/k selection theory works to explain some traits but not all of them. Obviously there are also more races than black, white, asian so the spectrum isnt so straightforward across all humanity. It works as a partial explanation for race differences at best

r/k slection theory was a favorite of Rushton. Ed Dutton is a more current proponent of this (partial) theory

Babies are still created from race mixing

Not relevant

but I think that r/k selection part is wrong.

I think you would be hard pressed to argue that blacks are not more k-selected than say, whites under the current welfare states in western countries (black dads never stay meme)