"The measure of IQ used in the analysis was obtained from tests of cognitive ability administered by the Norwegian military to all draft-eligible men at approximately the age of 19 y as part of the universal military draft in Norway. "
So they weren't even IQ tests.
So there are issues with the results, but the results as they stand seem to contradict current understanding.
Is the pdf significant or not? You'd need an expert to say.
There's also the fact that IQ tests need to be designed for a specific culture. Taking an IQ test for a very different culture is likely to cost you a couple of points. They're unavoidably subjective.
I think it could easily be a lot more than 10 points. I once (ages ago) did an IQ test from a book and then 2 days later did another test from the same book and scored 27 points higher.
From this I concluded that either I had become vastly cleverer over those 2 days or that IQ tests weren't a good measure of intelligence.