BetterThanOne saidThe railroad part (it's from Dumbo) is about how whites back then wanted everyone to believe that the slaves liked being slaves.
It's not a railroad, they're raising the circus tent. And they call themselves "roustabouts" which is a name for circus workers, and a more general term for any unskilled day laborers, such as on docks, in oil fields, and so forth. I'm not sure they're all Blacks, but it's true of the period that many such men were unschooled, and is an accurate depiction of their lifestyle, regardless of their color.
Disney was reflecting the standards of the day. And BTW, I don't believe those stand-alone film clips in the OP video were made by Disney, only the animations.
Such things are of course unacceptable today, and an embarrassment to see them now. One of my favorite old movies, Holiday Inn, which introduced the song White Christmas, has a terrible scene with Bing Crosby doing a number in black face. I cringe to see it, and wonder what they were thinking, even in 1942, spoiling an otherwise entertaining movie for me.
I'd like to read that Lies book, but I'm always skeptical about revisionist claims. Christopher Columbus, for instance, was indeed a very flawed man, but I'd like to hear their version. Part of our myth is that he was fighting the ignorance that the world was flat. Not at all.
The real scholarly objections he faced were that his calculations of the Earth's circumference were at least 3000 miles too small, making sailing West to reach the Indies an impossibly long voyage for the time, double what he predicted. The only reason he did run into something was because no one in Europe knew the American continents existed between them and the East, except for some vague and unreliable Viking legends that few alive knew. And even then Columbus thought he had reached Asia.
Columbus also later failed as a colonial governor, either because he was indeed an incompetent administrator, or else the victim of backstabbing rivals and slanderers. It's hard today to prove which was true. I'd be curious to see what that book says.