No matter if the car is moving or not, the sensor get jarred just hard enough, (NOT just "Jarred") it deploys it. And in THAT car, he just lost probably $1,000 with the cost of part, and labor.....
I know years ago, I had a Pontiac Sunfire (WILL NEVER own another one!) I was in an accident with another a car, and it deployed the air bag, and it costed $1,200 for the part and labor to reinstall it, and everything that goes with it!