higher IQ individuals having less children should lead to a decrease of average IQ, whereas the parent cites a reported 3 point increase per decade
As much as IQ tests want to say they test raw intelligence, education plays a major role in how well you score. And we are better educated as a society than we were 100 years ago.
When looking at IQ increase over time, you control for education and socioeconomic factors, otherwise you're just drawing conclusions from those factors.
How can you control for education when education itself has changed?