Transfer Terminal 3 from LHR flight to connection to Harbin

I am not sure I understand the following (under 'Tips') "For passengers of incoming international flights with domestic stopovers, they should proceed with passengers of international flights departing from Beijing at 4F of T3-C and wait for planes in T3-E."
My son is transferring from Air China flight from London (LHR) to domestic flight to Harbin (HRB), arriving and departing Terminal 3.
First time travelling to China - any help/clarification would be much appreciated :-)