Have you ever heard of a rebreather?
Of course - where is your evidence for one? You claimed to see a yellow air tank - not a rebreather. Are you changing your theory AGAIN? So you hear of a rebreather for the first time in your life, and now the mystery diver has one and not a yellow air tank? Too funny!
And please, where is the divers regulator? Nobody, but nobody, can scuba dive without one.