I don't think it's necessarily the turbo itself. The engine running at high rpms would have shaken it enough to disturb an actuator in the entire SRS system.
Just a hunch though- I have no idea where the sensors for the airbag are in the Supra or if it could even set off. That said, owners of Accords and Civics of all years have reported the airbag going off without even a single disturbance.