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.
There's probably some light painting going on as well with (bright) flashlights and long exposures.
The 1/r^4 really only applies if the light is coming from the camera position, and is unfocused. If you're illuminating the subject from another location, the only worry you really have is the 1/r^2 from the source to the lit object.