Access to schooling etc can't be the whole story: "black students from prosperous families tend to score higher in IQ than blacks from poor families, but they score no higher, on average, than whites from poor families".
So IQ is malleable and SES-dependent and GxE interactions are real.
No. The first part of that quote is consistent with any hypothesis (G only, E only, G&E), i.e. cannot distinguish between them.