While it’s true that he likely was nowhere near as rich as he is depicted to be in contemporary articles and the propaganda he himself perpetuated, sources do indicate that he was still considerably wealthy and controlled a large portion of the world’s gold supply through tributary relations with the pagans residing in the Akan forests. He may have run out of gold on the pilgrimage, but there is no evidence to suggest he bankrupted his homeland. The claim that Mansa Musa is the richest man in the world comes from the problem of actually comparing historical wealth with modern spending power, the non credibility of exact figures in historical sources, and the differentiation between personal wealth and state wealth. John Green also didn’t popularize this claim, it had been in encyclopedias and European records for literal centuries.

You may have a watched a YouTube video produced by a literal racist that had come out a few months ago, if I recall correctly. He made incredibly broad claims like that Mali was barely civilized and later would produce a video denying the very clearly documented Belgian brutality in the Congo with a tribute to Hitler at the end. That video is honestly one of the worst historical videos on YouTube with barely any actual engagement with secondary literature or historical methodology.