"But the plane’s pilots, as well as the airline, have raised the possibility that a key device that controls the Boeing 777’s speed may have malfunctioned."
I think Boeing would have been aware in the first week of the investigation if the autothrottle had malfunctioned, just as they were aware in the Turkish accident at Schipol. There has been no mention from Boeing of any autothrottle malfunction.
If the quote at the top is recent then it would imply that the pilots and the airline are still not aware of how the 777 autothrottle works. Although the autothrottle arm switches are engaged, and the autothrottle is engaged the autothrottle will not maintain the target speed in certain modes such as Flight Level Change if one flight director is off, the other is on and the autopilot is out and the flight director commands are not being followed. The warning is at the top left of the PFD where the thrust flight mode annunciation has gone to HOLD.
777 pilots (well most) have always been aware of how one can inadvertently get low and slow in this situation. The interesting thing will be if Boeing change the logic system of the autothrottle to make it easier for those who lack the basic skills. However by doing that they may be laying themselves open to the accusation that the system is not ideal and was contributory to the accident. The system does work well and if both flight directors had been off the autothrottle would have maintained the target speed and the accident would not have happened.