nah, i think it is because of their lack of focus at school work and that they in their family they do not incentivized to learn or achieve academically. matter of factt theres studies about that, cause after desegregation 12 years later there was a big lawsuit and it produced a study of why the underachieve at school it is called the Coleman study
and not quite, there are different kind of psychometrics and some are directly made to avoid that cultural "difference"
it's more done to know velocity in processing, even if someone has a vastly difference iq thy could still learn the same amount of things and achieve it's just going to take more time.
now to answer ops question, yes i do believe theres a genetic factor to intelligence, but no i think theres way to much of genetic factors involved that sometimes it kind of appears casually as proof of that, there are intelligent jeets and inteligent latinos and iranies and jews and such. now, the maps and graphs shown here are more likely the result of more "developed" nations being better at the tests.
as well, the test has been getting increasingly harder as education worldwide has increased. so its a combination of both of those not necesarilly.