This happened to us years back, in the bathroom as well. The difference was we were at home, so I turned off the main tap right away.
When it happened the noise was deafening, startled the crap out of us. Turns out the water pressure on those feeder taps is insane. Think: half a dozen regular taps open full-on all at once.
So yeah, this is why these upstream taps are (well, should be) sheathed with braided metal wire, in order to be able to tahan the continuous pressure. This braided stuff is strong and resilient.
That said, alas, nothing lasts forever. Eventually, even metal surrenders. The wire in our place exploded outwards at its weakest point. Out of nowhere, nobody was in the bathroom at the time. Its time had come I guess.
OP, in your case, you happened to be out, bummer. But if your piping is made from anything other than that wire stuff, I wouldn't outright concede to the LL's demands. Sure, you were out, but that's your prerogative obviously.
Bottom line, I'd be surprised if you don't end up splitting the cost with the LL, through legislation or otherwise. Still think the LL should pay the lion's share though.
Let us know you it went?
Good luck.
