But why would civilized people act like showing other people to zoos?
From a sociological point of view, this makes sense: a more technologically advanced civilization lacking modern-day sensibility and political correctness finds an ancient civilization living in the Neolithic, so they immediately assume that They are less than him. This has happened countless times in history.
In the Jiu Tang Shu (History of the Tang Dynasty) you can find examples of black slaves brought to China by Arab traders and slave traders, which were then acquired by wealthy Chinese people and used as entertainment by the nobility of Guangzhou. (for example they were hired as gatekeepers during parties to intimidate and impress the visiting guests).