The order from the zombie king had been shared with every zombie by the zombie queen in their minds. Zombies are undead types who gain intelligence only by reaching a higher level.
With the single command from the zombie king: 'Attack all at the same time!'
Every zombie in the vicinity, regardless of their levels, had followed the command. Like a huge wave made of zombies, the Ximen Mountain was besieged from all sides. With zombie generals in the lead, the zombies advanced towards the center.
The zombie king, Ye Yan, was looking at the whole scene from a bird's eye view perspective. A view from a high angle as if seen by a bird in flight. The system's authority allowed him to watch the events live and at this angle.
