This may well be a case of "everything went well under disguise".
I thought there were more than merely visual procedures in place to prevent this from happening, what about radio contact with the destination.
Weather permitting, a notorious customer requires a full 360 degress flight around the structure before landing.
Weather not permitting, if shooting an ARA, the destination has to be matched by the radar target.
Did the crew actually get a green deck or permission to land before landing?
I think there were likely other people sleeping at the wheel rather than just the pilots.
This could have been a potentially disastrous error had the structure been flaring or venting or some of the other stuff they do offshore when they do not want helos around.