I'm going to call bullshit on this one. We can't measure intelligence accurately now, particularly for people from non-Western cultures, and ESPECIALLY for people from the past. Every attempt do so ends up leaning on IQ, which is a notoriously fucked up and flawed way to measure intelligence that is inherently based on standards set by a couple of old guys with no oversight in the early 1900s (just like every other fucked up and flawed idea in the "science" of psychology). Attempting to measure the average intelligence of people long dead from a civilization long dead off of nothing but a few academic tomes is a fool's errand. It's the usual attempt by modern academia to portray everything from the past as unenlightened retardation.