Thankfully no one got hurt. What a blunder. 
I’ve drilled from my attic into a wall cavity and missed before. Even threaded 8 ft of Romex wire into the wall. Only to find it outside the wall and curled on the floor after climbing out of the attic. Oops . Time to try again and Spackle that hole in the ceiling.
Kind of funny that the construction guys make the same mistake with a 10 inch diameter bit in rock. How long was that bit? 20 ft or more? It’s like drilling a water well I guess.
Huh. Reminds me of David Macaulay’s wonderful book “Underground,” a hand-drawn explanation (for older kids and adults, too) of all the stuff below street level in a city – and how hard it is to do any kind of work without bumping into some previous installation.
The Chicago Loop Flood of 1992 was much more exciting - there a work crew on the Chicago River went through the bottom of the river into the top of a tunnel, flooding the underground regions of the Loop and River North, not to mention all the subway tunnels in the area.
I can’t find it now, but I read an interesting article once about a trenching company that ended up cutting in to the roof of a train car. They insisted there was no tunnel on the map they’d been given, which turned out to be 'cause due to city expansion over the years, they were technically on a bridge over a railway, even though you’d never know it.
At least they didn’t drain a lake into a salt mine like these guys: Lake Peigneur - Wikipedia
See also Lake Peigneur: The Swirling Vortex of Doom • Damn Interesting for more.
Looks like the MTA is now pre-drilling before they screw you.