The factory/airfield is the same CAC facility that they flew J-7s, J-10s, JF-17s, and J-20s out of when they all made their first maiden flights as prototypes and conducted their test flights, and it is also where new production aircraft do their first flights.
It is not abnormal for J-36's prototype (and future prototypes) to also carry out test flights from the same place that other prior CAC projects have done, it's just that over the decades the city of Chengdu itself has expanded to what was formerly the outskirts of the city.
It's pretty easy to geolocate where the video was taken -- yellow is the direction of the J-36 on final approach, red is the direction of the car from which the video was taken.
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The better question worth asking, is that chances are there are dozens or hundreds of higher quality videos and images taken of J-36 over its various test flights in recent times considering that the CAC factory/airfield is not exactly out in the hinterlands anymore, so why do we see so few pictures and videos of J-36?
The answer is that the PRC/PLA very much does care about secrecy, and most people know to not post anything too sensitive.