Was the climate different back then? How can one thrive in the desert
It spans huge across Africa. It's part of the same climate system and cycles as the Arab desert.
If an environmental feature leads to racial and species adaptations, you should note that its not some propaganda but an actual feature of physical reality that nature and mankind had to work around (and largely avoid).
You should also avoid assuming that everything is a conspiracy. Deserts are actually very harsh and deadly especially without motorized vehicles and modern infrastructure like paved roads and electricity.
They built canals for farming and understood how to use wild plants. Other cultures ( Akimel Oʼodham for one) are also interesting to read about how they lived.