The author never made this claim. In fact, the author writes:
"Your parents grew up 30 to 40 years ago in a poor third-world country. I don't care whether they came from China, Korea, Vietnam, or any other Asian country --- chances are that they grew up much poorer than the parents of your middle-class (probably white) American friends."
Well, for a few years in the early 80s they would have looked a bit more like a poor cousin of Mexico than a peer to an Ireland or Italy, and they would have been a military dictatorship, but I am sympathetic to the general point.
Yes, Mexico is a pretty good description based on the folks I've talked to that have been stationed in Korea in that time period. Hosting the Olympics (1988) apparently really brought some positive change, at least to Seoul. It surprised a lot of people, seeing open sewers and the like before and coming back some twenty years later to see all the changes.
"Your parents grew up 30 to 40 years ago in a poor third-world country. I don't care whether they came from China, Korea, Vietnam, or any other Asian country --- chances are that they grew up much poorer than the parents of your middle-class (probably white) American friends."