My guess is that a hot and high approach was flown in FLCH. That is the only mode that will get you down in a hurry. If the A/P is then disconnected, the auto throttles will remain in Hold, and not "wake up". If a pilot purely concentrated on the aim point and forgot his scan, speed could easily wash off to the point of stick shaker or beyond. FLCH is a major threat in the 777 if used while hand flying and should never be used during an approach. Our SOPs require FDs off, then one back on to force AT into speed mode.