What mode is the Boeing 777's autothrottle in right after touch down?
During the flare somewhere between 25' and 50', the A/T retards the thrust levers to idle. They remain in idle mode until reverse thrust is selected which automatically disconnects the A/T. 

In the case of Emirates 521, eyewitnesses observed the aircraft do a bounced landing and then attempt a go-around reaching a max altitude of about 150'. 

Because the aircraft had touched down, it can be assumed the A/T had automatically gone to idle, and it appears the thrust levers were not manually advanced. The aircraft then settled back on the runway as the gear was being retracted. 

More speculation here:  Emirates B777 crash was accident waiting to happen


  a pilot colleague observed exactly what happened as he was there, waiting in his aircraft to cross runway 12L. The B777 bounced and
  began a go-around. The aircraft reached about 150 feet (45 metres)
  with its landing gear retracting, then began to sink to the runway.
  
  This suggests that the pilots had initiated a go-around as they had
  been trained to do and had practised hundreds of times in simulators,
  but the engines failed to respond in time to the pilot-commanded
  thrust. Why?
  
  Bounces are not uncommon. They happen to all pilots occasionally. What
  was different with the Emirates B777 bounce was that the pilot elected
  to go around. This should not have been a problem as pilots are
  trained to apply power, pitch up (raise the nose) and climb away.
  However pilots are not really trained for go-arounds after a bounce;
  we practise go-arounds from a low approach attitude.
  
  Modern jets have autothrottles as part of the autoflight system. They
  have small TOGA (take off/go-around) switches on the throttle levers
  they click to command autothrottles to control the engines, to deliver
  the required thrust. Pilots do not physically push up the levers by
  themselves but trust the autothrottles to do that, although it is
  common to rest your hand on the top of the levers. So, on a go-around,
  all the pilot does is click the TOGA switches, pull back on the
  control column to raise the nose and — when the other pilot, after
  observing positive climb, announces it — calls “gear up” and away we
  go!
  
  But in the Dubai case, because the wheels had touched the runway, the
  landing gear sensors told the autoflight system computers that the
  aircraft was landed. So when the pilot clicked TOGA, the computers —
  without him initially realising it — inhibited TOGA as part of their
  design protocols and refused to spool up the engines as the pilot
  commanded.