I take it that inadvertant reverser on one or both engines is not a player? Not sure how to get to reverse thrust, but seems someone here can answer real quick.
Not familiar with the 767 but if this were the case here I would suspect reverser unlock and deployment would have caused significant yaw as per the Lauda 767 out of Thailand some years back. IIRC in that instance the result was in flight break up. You have very little time to catch it. The video suggests no noticeable roll, pitch or yaw changes.