I apologize if my knowledge on the subject is sub-par, but it seems as if third worldism is nothing more than third world nationalism, especially when put into practice. For example, I know RAIM has for the most part abandoned Marxism and now simply call themselves "third worldist" while pushing something of a third world nationalist "return-the-colonized-world-back-to-its-authentic-state-of-being" line (basically, replacing Marx with some weird Heidegger-Said hybrid). The LLCO (assuming they're more than just a guy with a website) claims to desire a "pan third world" movement which would allegedly offset racial/tribal ideology, but from there on they still promote many of the same nationalist and essentialist tropes.
The whole "return to an authentic, pre-colonized identity" as a strategy to resist imperialism sounds dangerously close to the ideology of NazBols. The predecessor to MTWism, Mirsaid Sultan-Galiev, based his proto-TWist socialism on this notion by claiming nationalist revolutions by Muslims, Asians and indigenous Africans and Native Americans would be "socialist" by default as these peoples had always lived communally before colonization. These tropes are also heavily emphasized in the ideology of Nazi Aleksandr Dugin and his "Fourth Political Theory" which bases itself entirely on Heideggerian philosophy (but the general idea is nearly identical). It's also not surprising how some of the regimes praised by NazBols, specifically Khomeini's Iran and Gaddafi's Libya, are also praised by third worldists, not only on the basis of "anti-imperialism" but on their ideological lines as well.
So to summarize: given its understanding of imperialism and how to fight it, how does third worldism remain Marxist and not become another hyper-nationalist praxis?