They deffinitely weren't miming, if you have heard the track on the radio (or bought it), you can spot the differences.
But if it's not the miming, it's the performance that was lacking anyway, or the stage presence, or they look tired, or something else...
People usually get annoyed at their lack of staging and jumping around aimlessly, so reading now that it's lacking enthousiasm or over-rehearsed is a new one.
I suppose to each their own: I enjoyed their performance & hope that people who didn't liked the other performances tonight.