Chu Hao had the Silver Dragon Armor, which was enough to support him in climbing Xintian Peak. And even though Yue Feng brought the Fair Bell with him, Chu Hao didn't need to use the Silver Dragon Armor during the fight—the minor achievement of Elemental Transformation was sufficient to cope with it.
He was only wary of large-scale attacks, but although Yue Feng's strength was indeed above his, Chu Hao absolutely didn't believe that even Yue Feng's wide-ranging strike could cause him serious injury.
Therefore, he was confident he was qualified for the battle.
He had such confidence, but Yang Jin and Dong Wei did not. They repeatedly tried to dissuade him—now that their master was in secluded cultivation, they felt responsible for this junior brother of theirs. If something happened, how would they explain it to their master later?
This was the genius who could potentially overwhelm Yue Feng and reinvigorate the Zhang Sect in the future.