I had CCTV video of a lightning strike near my office some years ago - that's exactly what it looked like on those old analog cameras at night. Instead of crumbling stone, I saw the image brighten a bit, then the aftermath - a smoking hole in the turf where it hit ground. Lightning hitting wet granite can absolutely cause that sort of destruction.
I saw it said that lightening can hit stone and explode it if it contains moisture.
Well... if it was lightning that would certainly explain why they cleaned it up so fast.
Wouldn’t want that getting out.