The ground below Seth shattered, making debris of concrete fly all over the place. People had to protect their eyes from the consequence of Seth's destruction to the ground. The force he landed with sent him two stories below making Seth find his destination on the top of a metal-like box.
He knew that this was the 'container' that Thress had hidden in. From where the demon prince stood, Seth could see the soldiers that had been stationed around the bunker die one after the other as the stones from the decking fell on them pretty hard.
The ones that survived the onslaught, upon seeing Seth, dropped their weapons and ran for their lives. They saw that as an opportunity since their commanders and king were all secured within the bunker. The soldiers left without thinking about it twice. Now, they knew that the false king was totally on his own.