Having flown the 777 for the company involved I can believe something like this could have happened, however some things need clearing up in regard to 777 operations. After T/O after acceleration height, FMA changes from TOGA to THR REF/LNAV/VNAV SPD ie. A/Ts set reference thrust on the engines, LNAV captures and VNAV speed is maintained by pitch attitude through the A/P or F/D which at this point is 230 knots (flaps 5 speed minus 5 knots) this speed is indicated as the target airspeed above the ASI (speed window is closed). If at this point FLCH is selected, again THR REF and LNAV unchanged, and FLCH is engaged, speed window opens indicating a target airpseed of 250 knots (below 10,000') and A/P or F/D maintains airspeed throught pictch angle.
There is no need to hand fly low level hold downs, the A/P has logic to anticipate this in FLCH or VNAV, and in fact at heavy weights close to the ground automation makes sense (even more so in that part of the world where manual proficiency is not maintained).
The 777 does have low speed protection even with the A/Ts selected off, and they would have enagaged automatically to prevent speed decreasing to near Vs (which even at heavy weights would be closer to 100 knots than 200 knots with flaps 15 still set). When the aircraft was accelerated using manual thrust and still climbing in FLCH the A/P would have mainted 250 during the climb, and any overspped condition would have been prevented by the load relief system.
To suggest pulling a CVR CB at the begginng of a 15hr flight is probably not prudent, as anything could happen after this point that could need to be recorded (ie. incident on approach), and the FDR would record all the parameters and selections anyway.
A valuable lesson learned hopefully for the crew involved, and I would expect that someone would notify the airline so that they can prevent it happening again.