Therefore, the prime suspect could only be the Skywalk Trading Company. Why the Skywalk Trading Company, you ask? Well, it's because they sent a Nascent Soul Ancestor.
The Skywalk Trading Company had both motive and ability. The motive came from a Jade Scroll that Li Shiming obtained several years ago, which was captured from a cultivator of the Skywalk Trading Company and which contained partial information about the Sect Protection Array of Qianye Temple.
As for ability, a trading company operating across continents would undoubtedly have special methods that no one would believe they lacked.
Why was the rocket launched from the Ten Thousand Great Mountains, yet it attacked Qianye Temple? Shouldn't Senluo Sect be the priority target, or even the Shushan Sect and Thousand Illusion Sect since they're closer?
The judgement from Qianye Temple was that someone wanted to incite hatred between the great sects.