VERY deep. You actually have to use a special air mixture to go much below 100 feet. (I went 110 feet with a “normal” tank, and even that was probably pushing it a little.) Other factors are involved, for example your weighting, buoyancy compensator, etc.
Deep dives over about 100 feet are dangerous enough. Deep cave dives are basically borderline suicide.
It was probably a screw-up or misunderstanding on the part of the reporter. Maybe they were 260 ft from the entrance. Hard to believe they dived to 260 ft deep - if they did, what the hell were they thinking? Nitrogen narcosis would be very likely if diving to that depth with normal compressed air, from what I understand.