The forebrain is the main processor. It does all the stuff you think of from OS to application, and has some ability to monitor and even interfere in the system management co-processor.

Whether either of these things have interesting internal structure and functional decomposition is left unaddressed. This observation about the progenitor cells is a bit like seeing the BOM that says they come from different suppliers.

I think it's also a bit of guesswork to try to reason out the evolutionary history. I.e. was either unit "in the market" longer and useful on its own, versus essentially complementary parts that just happen to have a divided supply chain! Intuition about evolutionary processes and life makes it really easy to assume the hindbrain is an older, legacy system that existed independently or with other long-lost companion units.

(Perhaps the updated title is less objectionable?)

...in a specific region, in a specific time period, immediately before the economic and then societal crash of the eastern Mediterranean that changed culture in the region forever.

The hypothesis breaks down pretty hard when you realize he just kind of handwaves away people in the rest of the world not having any kind of abrupt cut-over in the styles of recorded literature that forms the backbone of his arguments.