What are the laws that regulate flying around jails?

[MS Coast]

Yes, the Head Security Officer was the one that coordinated me testing the system. He was in radio contact with the security office, standing beside me, and they told me what drone I had in the air and where it was in relationship to the prison perimeter. I used my Phantom 4, Mini 2. and one of my Yuneec Typhoon H's.

They could certainly monitor your flights while not being able to control your flights. I'd suspect that DJI geo-fencing was preventing you from flying over the prison, not the system the prison was using, as @finity suggested. You might check to see if the prison appears on the DJI geo-fencing map.