Earlier quoted context omitted.
they’re making a (correct) point about causality and geographic gene variance
No, they are giving an absurd example in order to create the implication that heritability is a meaningless concept.
It's a practically useless concept outside of extremely narrow fields of biology, where you can control causes or otherwise eliminate genetic variation.
In the vast majority of cases where people use 'heritability', it is useless. Knowing how much a trait varies, or fails to vary, with genes tells you nothing about whether its inherited.
Under stable genetic equilibrium near universally inherited traits will have a heritability of zero; and under cultural, social, geographical etc. selection of mates, 0% inherited traits will be arbitrarily close to 100% heritability.
It's a statistics designed for cases where the experimenter is actually controlling the genetic variance (ie., breeding plants) across populations; it's otherwise meaningless.
Consider a security guard who forces all past shoplifters to wear a tag. Under such an induced causal relationship, wearing a red tag becomes predictive of future criminal behaviour. Otherwise, it's useless.
Likewise, when an experimenter is inducing genetic varience, then it becomes explanatory and predictive; otherwise, it's useless.