If a force of 1000 pounds hits a 1 sq in area (1000 psi) and is transferred to a 5” by 5” area (25 sq in), then the force would be reduced to 40 psi. A helmet is basically designed to spread an impact from a relatively small area and transfer it to a larger area. If your helmet hits a roll bar, steering wheel, pavement, etc., it’s designed to spread out the impact more evenly across the head hopefully to be less than the injury threshold.
Wouldn’t the opposite be true? If a pressure of 40 psi is applied to a 5” by 5” area (25 sq in) and is transferred to a 1 sq in area, the force would be 1000 pounds.
As the force of the airbag conforms to a large area of the helmet, it contacts the chin guard first, causing the helmet to lift at the rear, moving away from the forehead and near the chin. The result can be that the chin supports the force that is transferred through the helmet.
If the helmet doesn't rotate (which it does, even if properly fitted) and the chin alone doesn't absorb the increased force, then . . . nothing.