It's more the latter than the former, though it is a combination of both.

The third, and most prominent factor is that there was selection pressure for higher IQ in regions that were harsher to live in. Colder climates with less abundant food. Over time lower IQ individuals did not reproduce as much as higher IQ individuals did.

East Asia was full of subsistence farming of rice which is notoriously labor intensive. That gives rise to a culture that values those exact characteristics.