The part I find interesting is that according to the B787 drivers, both fuel switches cannot be switched off at once, unless both hands are used. The switch handles need to be lifted against spring pressure, to go through their locking gates. This applies whether you're selecting "run" or "cutoff" with the switch.
The drivers say it would require a person using both hands to switch both fuel switches to cutoff at the same time, as appears to be the case here. The fuel switch cutoff is instantaneous, the engine spools down immediately.
If the pilot or co-pilot, sitting in their seats, strapped in, tried to switch both fuel switches simultaneously, it would require some extreme body movement, to do so.
If the switches were moved to cutoff, one after the other, quickly, with one hand, I would expect to see some yaw, as one engine shut down before the other. I see zero yaw on takeoff, the flight travelled smoothly in one direction only.
As the switches are electric-over-mechanical, with spring pressure at the fuel valves holding the valves at the position they're set at (i.e., a power failure does not change the valve position), then the conclusion must be that electric power was supplied to the fuel valves to activate them to the cutoff position - and both at the same time.
How that could possibly happen if the switches weren't activated in the cockpit, has to be the main focus of the investigation, now. There is talk that the preliminary report, due tomorrow, will not reveal why the fuel valves were in the cutoff position - only that it happened, and much further investigation is going to be required, before the reason they were in that position, is found.