Once Li Qiye took a step backward, he returned to the present in the same spot. That’s why the emperor clearly felt his sword touching Li Qiye’s head earlier. 

It had indeed touched Li Qiye’s hair but because of his extreme speed, the slash felt so slow. Just by moving forward in time, the slash became nullified.

The emperor couldn’t read this during the heat of the moment but he could see this clearly now. That’s why he was pale because he notices that Li Qiye was standing at the door of the Everlasting...