He’s alluding to the ubiquitous misuse of the 3 worlds concept, though he’s also a bit wrong himself. It’s not about the 2nd world war but the cold one. First world nations are nations allied with or otherwise on the side of the “west” against the 2nd world which is the soviets and eastern block Europe while 3rd world nations are those that were largely uninvolved. Primarily the middle east and African nations who were mainly busy with surviving after having been left to fend for themselves after the end of colonial rule.
The term itself has nothing to do with the economic or developmental nature of a nation.