"....Ng Chi Ming, 40, went for a dive with 10 other people who were part of a diving company at about 6.40am yesterday.
After 10 minutes of diving and resurfacing, the dive master realised that a member of his group was missing, and searched for Ng in the area for about 45 minutes...."
Not sure whether the down current was happening here though, if 10 out of 11 divers didn't experience the down current. The down currents that I experience in Crystal Bay were spread wide enough that several divers would also experience it.
My speculation is he may not realize that he went too deep & got into narcosis, sank even deeper because things can get pretty calm & relaxing at the deep. No buddy was watching him.
The reason I say this is because I speak from my own experience. On my dive log #15 (my first open water trip, a total rookie), 12 years ago, I went pretty deep, 126' (38m) in dive site called Son of Rock Monster in Cayman Brac. Fortunately I was with a more experienced dive buddy who was watching me very closely. When we went into a crack starting at 60' (20m) deep entrance & came out of a 100' (30m) deep exit into the blue, I was fascinated with the good visibility & serenity of the surrounding without realizing I was sinking down to 126' until my buddy calmly gave me a sign to ascend (open hands with palms facing the surface and move down & up from waist to chest).