First, this apparently covers one single set of twins. Tiny sample size.

Second, I can't access the actual paper, but a commenter at Marginal Revolution wrote the following:

"Everyone in the comments here arguing about the implications of this study for the heritability of intelligence (vs. other factors like parenting) seems to be missing an important piece of information buried in the study: the twin raised in the US suffered three concussions as an adult, including one in 2018 that resulted in "light sensitivity and concentration difficulty" and led her to feel like a "different person, with increased anger and anxiety." It is hardly surprising that someone who has suffered multiple major concussions would score lower on tests of cognitive ability than someone who has not."