He's just using the zero-sum fallacy, in which some countries are rich because other countries are poor. It's an incredibly easy idea to deboonk, and the irony is if people start believing in zero-sum economics most people - especially non-whites - will just go full-fash. Even white (and "white") leftists aren't being genuinely altruistic since they get to reap the economic benefits of a slave class while living in enclaves where they're protected from that same slave class.

Meanwhile in reality we already know damn well that blaming third world poverty on colonization doesn't make sense. Because otherwise, Hong Kong, S. Korea, Japan, and many other East Asian countries would still be dirt poor. In fact plenty of countries across the world have gone from war-torn hellscapes and the sites of genocides to prosperous and peaceful within a few decades, even Rwanda is doing "well" (by African standards lol) and UK progs are trying to deprive them of that wonderful migrant labor - so selfish!