Killing a rank 4 magical beasts all by himself was a hard task.
Noah's dantian was still in the gaseous stage, it couldn't inflict heavy damages on creatures in the fourth rank and the "Breath" inside it wasn't enough to completely exhaust the beast.
Yet, Noah had the Demonic form spell which dealt damage over time and increased his physical capabilities.
That, added to the ability of his Yin body, gave him some sort of confidence in his battle prowess. Also, the fact that the Excavating worms were generally considered weak beasts further raised his hopes.
However, Daniel's group had changed the situation.
Noah couldn't use his large stash of potions or his "Breath" blessing to engage in a protracted battle with the leader, he would just attract the attention of the other cultivators in the lair.
That's why he decided that he had to be the first to meet the rank 4 worm.