The owner of the ramen shop and the employees he hired were all pure assassins. They didn't need to know the specific identity of the target or the reasons their employers wanted them dead; as long as the money was in the account, they would kill.
What Duan Mingyuan regretted was that the killers in the ramen shop were so pure that they usually hadn't even seen the faces of the employers, which prevented him from learning the employers' specific identities.
These were all details Duan Mingyuan found out afterwards.
He also learned that in Siyang City, there were many killers just like the ramen shop owner; the convenience store you've visited, the gas station you've passed by, and even the sanitation workers on the streets could all potentially be members of this assassin organization, and their means of livelihood was to dispose of people who were overly curious for their employers.
