The old Daoist who called himself Immortal Ziyang was naturally not a born ancestral spirit, nor was he an unrevealed Immortal concealed in plain sight; he wasn't even an Earthly Immortal.
So, when Gu Ximing's swords light illuminated at his waist, fully revealing his cultivation level, the face of Immortal Ziyang immediately underwent a drastic change.
When Gu Ximing entered, he had been suppressing his spiritual power aura, so Immortal Ziyang had no idea of Gu Ximing's cultivation level.
Similarly, because Immortal Ziyang had used some sort of Hidden Breath Secret Skill, Gu Ximing also did not know the old Daoist's cultivation level.
But since he couldn't see through him, this old Daoist must have had some extraordinary qualities; it was very likely that he was an Earthly Immortal just like himself. Therefore, though it seemed as if Gu Ximing had struck casually, he had actually used his full strength.