When his data shows that the average IQ in several functional countries are below what is considered to be mental retardation, it does call into question it's validity. I know we have a ton of abbos and chamars but honestly, even most of them aren't retarded. Slow, yes, but not retarded.
Also, there's stuff like Cambodia having a higher IQ than most developed countries, including ones where 'muh shitskin immigrants' isn't a statistically significant factor. Same for China, Belarus, Hungary and so on. None of those countries perform as you would expect countries with top tier average IQ to perform.