Great timing for the shot although you were clearly there long enough to see when you would have a good opportunity... anytime people walked by. Little concerning that it would be doing that all the time. Sounds like it could use more privacy so it feels comfortable with people around.
I fully agree about it being concerning. I found many of the cats at this facility to be perceptive and reactive to anyone walking by their exhibit. While it was enjoyable seeing the variety of animals here, their reactions left me with a very uneasy feeling about the facility.
I am friends with the owner of a major US cat facility. When I last visited his serval was doing this too and he said that is just how servals are - very hissy. So I would not be too concerned about this one.