He might have only been going under 14 mph, in a car than measures that, or other factors. Or... the magnetized ball bearing detectors have more leeway sensitivity for VERTICAL dislodge vs frontal impact inertial change. airbag non-deployment (ABND) is a complicated philosophical issue. A spurious deployment CAUSES fatal collision deaths, spinning cars into harm sometimes, so most airbags try hard to measure speed of car, and others ignore that and use other cues. GM gets tied up in this argument more than they should : https://www.safetyresearch.net/gm-airbag-non-deployments-what-the-nhtsa-data-really-show Deploy threshold speeds to ignore firing : > solid, fixed barrier at 8 to 14 mph or higher, OR striking a parked car of similar size at about 16 to 28 mph or higher: https://www.safercar.gov/Vehicle%20Shoppers/Air%20Bags/General%20FAQ