I haven't seen this exact documentary yet, but i have seen a documentary on this matter by Reggie Yates. i think the message will be similar. Problem is that white people in Europe start to know about marginalised white people in south africa and use it as excuse for racism. "racism is everywhere" "and what about poor white people in south Africa " they are saying when confronted with racism black people experience in Europe
you have right, it does not change the situation for black americans but it is relevant for our African brothers and sisters in south africa. We should take interest in each others issues, because only when we are able to be there for each others, we can ultimately change the narrative.