Saw the same thing on “This Old House” about a zillion years ago. They had a kerosene/oxygen torch with a stream of water shooting at the rock — they were texturing granite steps so they wouldn’t be slippery. The alternation of the hot oxy/kero with the cold water turned the rock to dust. They also used it to drill holes in the granite.
Old, old, old technology.
Worked on a system for a prof. from Vermont in the late 60’s.
1/2 in pipe w/diesel and a concentric 1 1/2 pipe and a few
hundred hp compressor.