“Oxygen tanks?
Are they using rebreathers or does the author not SCUBA knowledgeable?”
Huh?
SCUBA uses (with some exceptions) plain air compressed in tanks. A rebreather scrubs CO2 out, replaces oxygen, and recirculates the air. They both have advantages. The closed loop rebreather emits no bubbles and might be an advantage in cave diving by not agitating silt on surfaces above the diver which would hurt visibility. I’ve done some cave diving, never got out of sight of the entrance.