Earlier quoted context omitted.
The story I read indicated it was a planned "expedition", so presumably they had torches and such? You can't go far in pitch black in a cave and not injure yourself. It doesn't really add up as it's been told. The death of the expert diver too seems very strange.
What doesn't add up? Why is the death of the diver strange?
An expert diver who was delivering spare oxygen (or was it air), with a buddy, in a system in which a static line had been placed, and in which presumably a dive leader was managing operations and wouldn't allow a diver to return without a suitable amount of air .. in that situation they simply ran out of air? It seems so unlikely.
I just assumed that he got trapped, or carried by a current, or died in what might be perceived as a "stupid" way and they didn't want to mention it as it might hinder the rescue or sully the man's memory.
Maybe it's denial on my part.