Engineering cameras all over the bottom of the pad will probably be what they use. I'm sure they have high speed cameras looking directly up at the bottom of the engines like SpaceX has. They'll watch frame by frame and then confirm with sensor data or the other way around. Maybe a manufacturing defect caused a turbopump housing to rupture? The energy densities are so crazy in rocket engines that would probably be like 3 sticks of TNT going off. The propulsion engineers are intimately familiar with the engines they probably already have a good idea.