I cant recall exactly (and they have taken out the very specific mode/warning triggers from the 767 ops manuals)
this is unlikely given QFs stable approach criteria,
...but could it have been no landing flaps (ie they had forgotten to select flap 30) so they commenced a go around, during the go around as gear was retracted the gpws was activated. (I know sometimes in the sim you can get the spurious warnings as things take their time to retract).