It's that last sentence in particular that I think is important.The use of primitive culture has been used from the nineteenth century to the present day to justify colonial appropriations. It is inherently judgmental and used to assert the intellectual superiority of the West (in which technological advancement was associated with the concept of "Civilization"). It treats contemporary people as if they were in the "stone age," and thus relics of a different era, minimizing their knowledges and world views. Until the mid 20th century (at best), the "primitivism" of groups was thought to be biologically determined.
As I've tried to set out in a few recent posts in this thread, there are good theoretical frameworks available for thinking about processes of the diffusion of technology. These weren't available to the "scientific" racists - they emerge out of the sociology that is developed/invented in the second half of the nineteenth century and the early part of the twentieth century; which is to say that they emerge during the heyday of "scientific" racism.
Once we have these theories available, we can see that biological explanations are (i) silly and (ii) themselves the expression of the sorts of ideological processes that good sociology explains.
And we can also see that to the extent that FRPGing clings to these sorts of biological explanations - as it clearly does, per the discussions in this thread and especially @Doug McCrae's exegetical work - it is rejecting realism in favour of racist tropes.