The Jungle was quite literally built around a skate park and the surrounding area. Its defenses were quite meager, chain link, barbed wire, and watchtowers. Though there appeared to be some effort to reinforce these "walls" via the means of the settlement management feature.
Aside from this, the area had tents, and other forms of shelters spread throughout it. Some built by the system, others build by hand. The exact origin of the Jungle was unclear to Zane, or why a settlement had been built here. But he didn't express his concerns about the viable safety of the area.
No doubt, the local Horde King was aware of the human settlements ,but for whatever reason not interested in wiping them out. Perhaps as a form of entertainment, it was really hard to tell when one had met the undead in charge of this city.