You raise some really interesting points. I've seen similar as well. But what I draw is not so much that there's an IQ gene (though I'm sure that there are genes that affect brain physiology in some ways), but more so that there are known genes that affect compulsive behaviours which can trump rational processes e.g. addiction, risk-taking.

And while I'm sure lifestyle factors (including nurture, environment) may impact the "degree" to which the expression of these genes "take hold on behaviour", the overall probabilities are more likely to be based on the genetics. I'm thinking similar to how genes increase likelihood of getting cancer, while behaviour/lifestyle can affect treatment outcomes.