Apparently it's a big deal to you.
It's a monumentally big deal for him! They absolutely cling to seeing people as black or white. And, then whenever possible, exploiting that aspect as far as possible in order to judge anyone that is trying to STOP seeing them as black or white. And, that flag REALLY gets their dander up. Racism is cool with them. They revel in racism. They count on it. But, that flag is not cool. The irony, of course, is they need that flag to continue on this crusade to stop racism that they love to perpetuate by identifying people as black or white.
The people in the video clip are basically the result of the perpetuation of people seeing each other as different races, not as fellow human beings. The people dragging that flag, and the other flags, around were trying to incite the other people. The other people responded as expected. Until one of them stops, they will both keep doing it.