When John initially went through the original Li Wei's memories, he kept track of several relationships and people that he might have to deal with or encounter in the future.
Four people in total. Li Wei's only friend, the black market dealer who originally got him into the sect, a servant who fed him and lent him money when things were extremely tough for the both of them, a fellow disciple who he beat up after a conflict causing a feud between them. There were others that might resurface, such as his family, some other friends and aquaintances, even some debtors, but overall only these four were in the sect.
If the one knocking wasn't one of the four, then it could only be someone with ill intentions.
Ending his cultivation, Li Wei got up and opened the door, immediately he breathed a sigh of relief.
