If I remember correctly, go-arounds in the 777 begin with pressing the TOGA button, (on the throttles) which both rotates the aircraft ( with the autopilot engaged) and gives you go-around power. Also, if I remember correctly, touchdown disconnects the autothrottles. I can fully understand why the crew was surprised that the autothrottles did not advance as they expected if they had never practiced a go around after touchdown.
Joe