When Ken saw that the library was guarded by a hundred Nascent Soul cultivators ranging from the low phase to the peak phase, he started forming a plan to get past them and enter the place.
As soon as he saw the approaching guards, an idea hatched in his mind, and he carried it right away. By killing the 3 guards but leaving one alive, he allowed him to call for help and pull everyone's attention to him.
While both the guard who called for help and the guards hearing this call thought Ken failed, they fell into his trap. The guard was acting as a messenger for him.
He then stepped into the water and ran toward the center, making the cultivators from the Infinite Wisdom Sect think he was trying to force his way with a straight charge while dodging incoming attacks and maneuvering between their techniques.
