First off the Transport safety board will determine what happened. The crew and passengers will be interviewed. The ship will be inspected. Weather conditions will be noted. As in the majority of incedents, it will be a combination of factors.
My guess is “stability” played a part. As did a “rouge” wave. Passengers have reported that “nobody saw the wave coming”. That suggests compacancy may have been in play.. It should be noted that being an “armchair” sailor is easy and easily wrong.