Re: Physics Says...
"As pointed out above, it seems* more likely that the problem was a loss of pressure"
Elon Musk tweeted that, "There was an overpressure event in the upper stage liquid oxygen tank. Data suggests counterintuitive cause".
I'm presuming that if there had been a puncture and loss of oxygen or something else that provided pressurised structural integrity he would have tweeted accordingly, but he didn't.
We'll see what the counterintuitive cause is thought to be sooner or later.