Don't bother speculating
"Okay, if this is a rumour network, what possible causes do we suspect given the witness accounts? "
Speculating, in my opinion, based on observations of similar accidents, is a waste of time. Don't trust "eyewitnesses" - stick them in front of a TV camera, or a reporter, and they say any old rubbish.
Be patient, wait for the facts, once the dust has settled, and make an informed judgement if you wish, but you will be wasting your time if you attach any credence to early "eye witness" reports.