Because he hadn't been maintaining his spiritual network consistently, the demon man didn't know what had killed the chunks of flesh he had split off.
Feeling the flesh worms rapidly dying, the demon man released his Spiritual Power, connecting to the flesh worms, attempting to "see" the one who killed them.
But in his "eyes," the demon man only saw a flash of golden light before the "eyes" disappeared, completely unable to see his opponent's form.
"Flame?" The demon man thought of the man who had instantly killed him, shivering involuntarily inside; that man possessed the abilities of ice, fire, and flight. He had only witnessed the man's ice, the kind that could freeze one's soul unstoppably, too terrifying.
As for the flame, the demon man hadn't seen Lu Yu use the Celestial Falling Bright Flame, so he didn't know if the golden flame user was indeed the man who froze him.