Thunderf00t does another videos, looking at the audio from the explosion.
He makes a good point about that popping sound. Especially in light of this:
At this stage of the investigation, preliminary review of the data and debris suggests that a large breach in the cryogenic helium system of the second stage liquid oxygen tank took place. [Updated 09/24: At this time, the cause of the potential breach remains unknown.] All plausible causes are being tracked in an extensive fault tree and carefully investigated. Through the fault tree and data review process, we have exonerated any connection with last year’s CRS-7 mishap.
The popping sound is telling. That is a pressure vessel breach. Likely what happened is that the liquid Helium wanted for some reason to become gas. When this happens, the liquid HE wants to become the 1000 times less dense gas. This happens very fast and there are no rupture systems that are fast enough. The 6000 PSI mentioned was the normal operating pressure. There’s a good chance that the pressure at rupture was ten times that, and the event was not going to be over until all the gas vaporized. Which it did, taking the liquid O2 with it. There is no exact science to pressure vessels and even thought the technology is very mature, they still fail for unexplained reasons. A mild thermal stress between the 4k liquid HE and the approx. 100k LO2 might have been enough. Or there was a void in the composite tank. Or even a broken fiber. At this point there’s no easy way to tell. Well nobody was hurt and the satellite was insured, so the best thing to do is go on. Learn what you can from the wreckage, but understanding that there are never any perfect engineering answers.