The disciple of the Space God didn't know if Ange was telling the truth or it was just a bluff to scare him, but he had lived long enough to know that regardless if Ange told the truth or not, she was still strong enough to make him take her seriously on the battle.
The area had been sealed, so the option of fleeing was impossible. Thus, he could only risk his life and hope that Ange wasn't as monstrous as she said she was.
As for Devy, he had decided to ignore her. He knew that he wasn't in a situation to care for that girl, and the area was isolated anyway, so he didn't believe that she could flee.
Ange didn't seem to be in a rush to finish the battle, so her opponent started to think that she might have exaggerated about her own power, but even after several days of battle, she hadn't received a single blow from him, which showed that at least, she was a real threat.