I have a different take on it. They know they have done our people wrong for hundreds of years, and in their consciousness they need to justify their actions somehow. So how they do it is by making it seem we deserve what happened to us. One of the ways they seek to accomplish this is by putting out there that we have never been anything but slaves.
So, when anything goes against that narrative of us being lower than them, and worthy of being mistreated, their mind goes into conniptions and they desperately work to hide, remove, or downplay the truth. Add in the fact that many of them only have the thin veneer of Whiteness to make them feel good about themselves, I can see them going through all sorts of actions that make no damn sense in order to maintain their feeling of pseudo superiority.
I think one thing that can be done to counter it is to remind idiots like the Brazilian on that video, that he has not personally accomplished anything. That his only claim to glory is to believe the accomplishments of others in his race are a representation of his own worth. Remind him that even his own people feel he is trash.