It was not.
The South African policy of "separate development," as it was admittedly euphemized, was not a theory of racial supremacy, but a strategy for survival.
But first: To perceive the fundamental way in which the Afrikaner and American creeds differed early on we must first examine the former’s ideas of what a nation and a state were, respectively.
America, being a rib from the British ribcage, was built on liberal individualism; Afrikaner culture was first and foremost grounded in the survival of the Volk.
See 'Battle of Blood River.'
This is not to say that Afrikaners were not fiercely individualistic; they were, even more so than early Americans.
For the Boers, however, the nation encompassed "the land, the culture, the terrain, the people." The state, on the other hand, had no such prestige for the Boers, who regarded it as just "the coercive apparatus of bureaucrats and politicians." Against this apparatus, above all, the Boer rebelled.
The 19th century found him still resisting majority rule, by which time Americans had thoroughly submitted to it. Although the Boer’s outlook remained passionately political, his preference was for parochial self-rule.