If the threshold has been moved, is this recent? Would the FMC nav database still have the previous threshold? This obviously should not cause landing short but would contribute to destabilising when low and in a low energy state.
Were the two relief pilots in the cockpit? Wonder what they were thinking?
In addition to thoughts for all on the 777, I feel for those on the aircraft at the hold point. Not nice to witness something so terrifying and so close. Been there.