The flight and voice recorders seemed quite definitive but this is not something you can easily do by mistake. You'd need to put quite a bit of force to pull out the stick and move it to cut-of position. There are also metal brackets on the sides that prevent you from accidentally touching it - which was an issue on older planes where the stick could just be moved without pulling it out first and was a physical rather than electronic switch.
Pilot also said he didn't move it when asked. And there would be no reason for anyone to touch those switches in flight. They are to start/shut down engines, so generally only touched on the taxiway and at the gate, except in case of engine fire or detachment, etc.
Had this been older plane like 737-800, yes, it was possible to leave switches in position where vibration could accidentally move them to cut-off but not on 787.
Some serious questions. How could pilot switch (which is, if you have a manual car, equate to unknowingly pulling up the gear shift stick and moving it to reverse position) to cut-off without realising it, or, does the engine controller have the ability to physically move the switch on its own? If the latter, there would be a deadly flaw in Dreamliner engine fuel control system. If this was pilot error... I just can't see how this could be accidental. It borders on impossible.