Unintentional activation of “cruise control” at the wrong time and speed.
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Seems like it got hacked into and someone outside took control...
A faulty processing unit could have randomly commanded the cruise control system to enter into a rogue-ish mode where a previously established cruising speed can be temporarily overridden in order to bring the speed up or down and reset by the driver to a new cruising speed. If the driver never establishes that new cruising speed, an uncontrolled sustained acceleration of the vehicle may occur. This is just an “educated” guess on my part and if I’m even close then I’d like to hear what Bentley Motors LTD would have to say about it.