I wonder how they took the pictures. Was there enough light in the cave thru some holes in the ceiling? Did they install huge lamps or did they use a very long exposure (seems unlikely by looking at the people). either way stunning and surreal photographs!
In particular, note the shot of the row of people under the low ceiling. Each person has a hotspot that illuminates the ceiling and silhouettes them; the person is in between the bulb and the camera. In other words, the lights are all oriented the same way, which suggests to me they were set for the shot, rather than being the chance arrangement of the cavers' utility lights at that moment.
They might have used long exposures, but the people aren't blurred, so the exposures can't have been all that long.
Then again, flash would probably be murder on the eyes for cavers, so maybe these were less-bright-than-flash lamps, with a slightly-long exposure.