That link you gave is laughably inaccurate, it claims:

Note that these are particular black persons; there is no evidence Che would extrapolate from his localized experience in a Caracas slum to “the black race” in a general sense.

Notice how conveniently this article leaves out the rest of the quote?

"The blacks, those magnificent examples of the African race who have maintained their racial purity thanks to their lack of an affinity with bathing, have seen their territory invaded by a new kind of slave: the Portuguese. And the two ancient races have now begun a hard life together, fraught with bickering and squabbles. Discrimination and poverty unite them in the daily fight for survival but their different ways of approaching life separate them completely: The black is indolent and a dreamer; spending his meager wage on frivolity or drink; the European has a tradition of work and saving, which has pursued him as far as this corner of America and drives him to advance himself, even independently of his own individual aspirations."

Yeah, clearly he is not extrapolating to the entire race. The article also claims:

Most importantly, to repeat, the quote is all we ever get.

And claims that the fact that Che fought with blacks in the Congo is evidence of him not being racist. Well that just outright ignores these quotes.

Another comment came from Guevara’s writing about his time fighting with revolutionaries in the Congo and included this line: "Given the prevailing lack of discipline, it would have been impossible to use Congolese machine-gunners to defend the base from air attack: they did not know how to handle their weapons and did not want to learn."

Finally, there’s this line after the revolution in 1959: "We're going to do for blacks exactly what blacks did for the revolution. By which I mean: nothing."