The airbag will trigger when the sensor measures a decelleration over a specified amount. When the crumple zone crumples, it has two effects. 1) It dissapates alot of energy and dramatically reduces the decelleration encountered by the passenger, thus making it less likely that the airbag was needed 2) It makes the car look like it was hit by a train.

I’d have to guess this is a case where the crumple zone makes the accident look worse than it was, especially if nobody was hurt.