The Flynn Effect is what we call the phenomenon of IQ rates going up across the board over the last 75 years, it's established as true yet nobody will claim that we all got genetically smarter.
https://en.wikipedia.org/wiki/Flynn_effect#Possible_end_of_p...
The study you linked was interesting but adopted kids are an abnormal case to begin with and the effect indicated was tiny compared to societal things IMO.
However, a ray of hope in the study is that, even if you take its confidence intervals at face value (I don't), then there is quite a bit of room for improvement in the nurture sphere, as the black/white IQ test gap is generally much larger than this when not as carefully controlled as this study.