No, it was Our Lady Good Counsel High School from Maryland.
St Mary's was rated #1 in the Nation by all the rating services so it would not have been an upset if they beat Mater Dei. They beat Mater Dei last year in the California Open Championships and have almost their entire team back. Where as Mater Dai lost the top player in the country K. L. Samualson and their top point guard. Mater Dei is not the team they were last season. They would be really lucky to make the State Championships. Quite a few teams in southern cal that are much better than they are.