Being a "third world country" has nothing to do with affluence, and everything to do with not being aligned with either NATO or the Warsaw Pact.
WTF dude? This is a totally pedantic use of the archaic definition of the "third world" and has no bearing on modern reality. Back in the 60s "third world" referred to countries not part of the cold war, but since then it has commonly referred to poor, developing, or "emerging market" economies which are by definition NOT on the list of highest GDP per capita.
I see three different lists presented, and none of the countries in the top five count as "third-world" by the modern definition. Norway? Qatar? Singapore? These are thriving first world nations.