But to your criticism, the transition from "vaquero" to "cowboy" just reflects the influence of Spanish culture on American ranching practices.
Vaqueros and cowboys worked side by side so it seems to be a natural transition between the two and has much more support historically and linguistically than the complete lack of evidence provided by the article.
Words don't appear out of nowhere, they naturally evolve and generally are based on imported words and root words, and it makes sense that Spain, the ones who created this practice and imported these cows and horses were the root of the evolution, beginning from the latin root word "vacca".
Black cowboy culture is kinda lost from the popular narrative - and cowboy culture was anglicized to an extent that the Mexican origins were also buried - similarly both mexican and black folks experienced similar kinds of racism depending on which part of the state they were in.
FWiW, though, The Adventures of Buckaroo Banzai Across the 8th Dimension (1984) predates Space Cowboys (2000) by a good 0x10000 years; this ties in Hollywood, westerns, two chronological points and binary.
The term cowboy seems to have occurred naturally as a less literal transition of the word vaquero.
I am not a linguistics expert though, there may be someone else that has more details on the transition.
I will also accept a fortification of the article's attempt at explaining the origin, but I don't see any evidence or attempt at providing any.
Also as I noted in earlier comments the word "cowboy" was being used in print in 1725 by that time and used heavily in the British Isles in the mid 1800s
Many words that were in print in the 18th Century have since been used in different contexts and taken on new associations.
Judging from the theme and tones of their articles and their lack of evidence in their claims it is of my opinion they are race-baiting.
That is a subjective view so feel free to interpret their motives as you wish, I will interpret them how I view them based on my evaluations.
The thing is, you can motivate almost any oversimplified narrative with mutually exclusive rationales. Maybe you claim that all cowboys were white because you’re racist and you don’t think black people had the heroic qualities necessary for herding cattle. Or you could claim that all cowboys were white because the evil white man didn’t allow blacks to settle the frontier. I actually think this story is more on the side of nuance: it turns out some West Texas cowboys were black, some were white, and people on the frontier didn’t have the same obsession with maintaining racial systems of social hierarchy the way people did in the Deep South. Some of them would still be racist but a black man could handle those differences the same way men in that culture handled many of their differences, with his fists. And when this particular black cowboy did that, it worked out fine.
The odd claim about the etymology of the word “cowboy” does sort of hint and edge towards a completely different totalizing mythology of “actually, all cowboys were black”, but this also smells like bullshit to me. There were almost certainly more black cowboys than you’d assume based on watching old westerns, but they weren’t all black and none of the people in that place and time comfortably fit into any side of any contemporary culture war anyway. They were different people with ideas and motivations of their own, not just symbols in your contemporary culture war.
Regarding the other terms that were in use: Cowhand, ranchhand, drovers, stockmen etc etc. - does the use of these terms disprove the racialised aspects of cowboy or the story of how the word became popularised? I would think cowboy could have still been popularised in the slavery context despite not having been coined especially for it.