That wasn’t in dispute. Yours started with"they weren’t breathing compressed air " which you had to row back from when I pointed out that you couldn’t breathe uncompressed air at 6 metres from the surface . (Wrong statement number one).
Secondly you claimed that breathing air from a tank at that depth was physiologically different from breathing compressed air from the surface at the same depth (Wrong statement number number two) . The second stage demand valve they are using supplies air at ambient pressure relative to the depth ,so is irrelevant which source it comes from. What you have quoted there is irrelevant to that point and the conversation we were having despite it being factually correct and which I never disputed. In summary it is a complete deflection to the two incorrect statements you made (the first one a complete howler ).