when a plate moves there is more than one side Sure... but that doesn't mean the whole plate moves. If it did... you would notice more than one earthquake.
Also, I think it was the Indian Ocean side of the fault that slipped - different plate.
Try again dear. The subduction quake occurred along an approximately 600 mile long front. The epicenter was, as illustrated, in the extreme eastern Indian Ocean. had there been a simultaneous "other side" quake,
two epicenters would have been detected and plotted- not just one.
The going aground of this submarine was not related in any way to the earthquake.