Hard to imagine what would capsize a ship this size short of a hurricane.
Highly unlikely that it capsized in the classic sense. Everyone was saved, they had time to evacuate to the boats, a distress call was sent out. Knockdowns and capsizings happen too fast for all this to take place. It was also a fairly modern vessel with generous freeboard.
Given the weather conditions reported, most sail was probably off so she would have been essentially a power vessel at the time. This will most likely turn out to be a classic case of a vessel being gradually overwhelmed by water infiltrating through numerous deck openings and systems due to ineffective damage control and crew management. It's happened to larger cruise ships.
At some point, the water rises high enough to compromise the vessel's stability and it may even capsize but it is a very different kind of accident than the Pride of Baltimore, Marques, and other ships that were blown over suddenly due to inadequate stability.