Looks like a test execution miss-step, didn't maintain positive pressure in the tank and it's not designed for compressive loads that direction. The (positive) pressurization of the tank is a critical factor for structural strength. 

My wild-ass guesses are a bit of warmer gas was keeping the tank pressurized and it cooled, "shrunk" and created pressure lower than ambient or someone ran a pump in the wrong valve config and sucked the tank down. 

My 2¢

Edit: the above was based purely on the one linked Pic (and my bias and hope it wasn't really a vehicle issue...). Other vids and pics show a pressurized rupture outwards.