surely not: My guess is that not all the pax will have proper travel documents, therefore the police check compares photos and details on file against the person travelling on those details
Pure guess, but it makes sense to me
It would make sense if the police had come on and eyeballed everyone, but the OP suggests that they didn't. Which made me think that this was a manifest/paperwork check - hence the puzzlement as to why it couldn't have been electronically transferred over after the aircraft's departure from SIN.