Same story as in plantation times: Make the white servants feel superior to black slaves by virtue of skin color; manipulate poor whites into believing that any perceived gains by blacks had come at their expense.
Although the absolute wealth of poor might have improved since 1900, people can still be angry that someone is extracting disproportionate amount from the system while their situation is stagnating. See flatlined real wages since 1970s
Like many pointed out here, this "43%" was nothing special this year if, for example, you are mid-career and have moderately aggressive stock market participation. It's an example of headline entirely cooked up for agitation.
You are right, it's not the majority of the population. The fine article was trying to raise indignation at the wealth increase of "the 25 richest families in the world", using seemingly gross numbers that they militarized without even noticing that these numbers were completely unremarkable. Or perhaps in bad faith altogether.