I came across a video on Youtube discussing it (there are several), and Kowloon Walled City is just endlessly fascinating. A few notable videos I found on the subject were:
There is also a book on the city called City Of Darkness Life In Kowloon Walled City, which I found on archive.org in high resolution. It is full of photographs and detailed accounts of the comings and goings within the enclave.
Curiously, in cyberpunk media this sort of mega-slum is often portrayed as an excess of capitalist urbanization, whereas in historical reality it was an exclave of "communist" China inserted into "capitalist" British Hong Kong, wherein the "capitalist" authorities had no jurisdiction.
(Edited: Sounds more like the point was that it was effectively nobody's jurisdiction.)
What the fuck are you talking about? In actual reality it was a product of capitalism. Specifically British imperialist capitalism in China. It took until the mid 80’s (40 years after the Communists came to power) for the British to allow China to have control over the area and it was turned in to a park less than a decade later, clearly indicating that the Communists were in no way interested in continuing the existence of the dystopian walled city.
With no government enforcement from the Chinese or the British aside from a few raids by the Hong Kong Police, the walled city became a haven for crime and drugs. It was only during a 1959 trial for a murder that occurred within the walled city that the Hong Kong government was ruled to have jurisdiction there.
The KMT repeatedly sent requests to reclaim the entire region but Imperial Britain pretty much refused (they proposed a ton of alternative solutions) and didn't govern it either. So yes, it's Imperial Britain's fault. Since the day Britain agreed to transfer the territory to the CCP there was a declared intent to demolish the place.
It's more accurate to say that the British prevented either themselves (through inaction) or China (by treaty/law) from having any practical control. If you'd bother to read the wiki article OP linked you'd know. China should have had jurisdication, but Britain techincally had (imperialist) jurisdication. The result was a no-man's land until Britain finally gave up.