actually a lot of this is like the terrorist handbook of getting around airport security
Hong Kong and other airports suffer from the boarding pass ticket switch system operated by syndicates
A triad checks under Mr Y in and enters the secure departure area
An incoming client enters the departure area in transit having managed to get there as Mr X
In the loo , conniving sales people or elsewhere Mr X gets a new passport in Y's name and genuine boarding pass and hopefully then goes on to his destination of dreams
Triad says his wife in an accident and is escorted out through security/immig/customs
Hopefully the computer system can pick this up
It could also mean a jihadi gets on the flight.....

Also, as HK resident I have only tried to use the Arrival (not operated by CX but a lounge contractor) once - I was told it was only for incoming flights from certain long haul destinations (I came in from Vietnam on CX Biz as a Diamond member)