If I had a lot more time I'd like to take a longer look at that link and make a list of all the fallacies and dark patterns it uses. As it I just managed to glance that it first sets up a narrow, technical definition of heritability which then proceeds to criticise. That's a pretty standard dark pattern.

Whatever his definition is, what we mean in this conversation is that smart parents tend to have smart children, and dumb parents tend to have dumb children, and that there's little one can do with the environment (besides minimum nutrition) to change that.