Yes, if you're inverted but the force vector points towards the plane floor, that means the plane is accelerating towards the ground (for example if it's flying

Yes, if you're inverted but the force vector points towards the plane floor, that means the plane is accelerating towards the ground (for example if it's flying a loop). And if you just fly straight and upside down, of course the force vector will point to the roof, not the floor. The problem was the plane making an unintended coordinated turn, which happens in the cloud. The nature of the turn is such that a human or a level can't detect it.