The one attack from Yu Sheng drew the attention of a small number of people. That guy seems very powerful as well, they thought. Furthermore, he never bothered going out to fight on his own.
Shen Jun was somewhat relieved. Those two he had deployed to test Ye Futian's party out were half-saints and were very proficient with the art of the blade. Yu Sheng was so terrifying that he had ended one of them within mere moments. That was the reason why he bet on Yu Sheng.
From his perspective, so long as Yu Sheng practiced caution and worked with those around him, there was a significant chance that he would end up breaking through. Thus, he was worthy of being betted on.
Yu Sheng did not bother following up with his attacks after sending that one person who came at him flying. He also did not seek to fight any of the others, and simply remained behind, holding the fort down.