This paper and line of research is famously garbage. It's based both on Richard Lynn's fraudulent numbers (I have a hobby-horse on HN, and it is pointing out that no country-by-country study of "national IQ" has ever been performed --- in this one case, we'll leave "how then did Lynn come to claim that data existed?" as a question for the reader, but it's got some fun answers) and on a handwavy claimed correlation between GDP and IQ (the Koreans would like a word).

Nonetheless, once a clever-sounding claim like this hits the message board ecosystem, you never hear the end of it, and it's a favorite argument among a certain cohort of motivated Internet commenter.