I don't know enough to make a very good guess, but let's use the situation that Escaped Lunatic was in that led to his having to get that ridiculous security system.
He was living quite happily with his wife in his dream house in an integrated part his village somewhere in the vast expanse of Dongguan for what, I can't recall, months? years? One evening he went to some social gathering and was seated at a table with the local bigwigs who had assumed that Sir Laowai was segregated with all the other evil foreigners, but were wrong. Upon discovering their error, they immediately began enforcement protocols.
One could say that in EL's case there was a profit motive, I'm not suggesting racism, but merely saying it's an example of people who should have known not knowing.
Maybe one of the decision makers in your uni was vaguely aware of the Africans teaching, then he saw an important CCTV news story about evil, drug-trafficking Africans in Beijing, and he suddenly decided, "No more! They will dilute the purity of my university!"
Anyway, I don't know enough to guess at specific patterns within your university.