Wu Chang could have just left the Demon Realm and informed Shuanghu City, so that the cultivators in the city could prepare the Teleportation Array.
The reason he didn't send a message and suddenly returned to Shuanghu City was to catch the cultivators in Shuanghu City off guard.
The fastest way from Zhenyue City to the Demon Realm is to teleport to Shuanghu City, and then enter the Demon Realm from Shuanghu City.
Long-distance Teleportation Arrays consume a large amount of Spiritual Qi each time they are activated, and are not common tools, only activated for urgent matters.
If the human cultivator who communicated with the Blue Feather Bird acted alone, there would definitely be a record left on the Teleportation Array.
If the informant cultivator was colluding with the Shuanghu City cultivators, seeing Wu Chang and others return, the spies left in Shuanghu City would definitely inform and try to erase the records of the traitor using the Teleportation Array.
