Only thing I can think of is explosive blowing the engine downwards. The engine and transmission are very heavy, there should be tell tell marks on the road telling how it traveled. But I can remember seeing the car crash on tv and not knowing anything about the situation and thinking I never see a car fire look that intense.How does a car leave its engine and drive train behind and then blow up and burn????
The engine and transmission is the densest (highest specific gravity) objects on a car - they would be likely to continue in the path of motion in any collision.
There is something very uncomfortable in this.