Zhang Quan was a spy that Kunlun had planted within the Mortal Life Path.
In this world, counterintelligence technology simply didn't exist, so it was a matter of course for the great sects to embed moles within rival sects, without the need for debating the legitimacy of such actions... After all, if there truly were some sort of lie-detection magical treasure, it would definitely be placed in the center of the square by the sect leaders for cultivators to test themselves with daily.
Under such conditions, the Kunlun Mirror would not take a fancy to someone so easily.
There must be quite a few spies like Zhang Quan in the Mortal Life Path.
It's just that he didn't know exactly who they were, for spies needed to be inconspicuous and keep a low profile.
If Zhang Quan knew who the spies were, it meant that there was something about them that aroused suspicion, and such individuals often weren't far from death.