need info...
Welcome to the TDR!
What year is your truck? It is possible one of the sensor wires was damaged in the alignment process by the mechanics. It could also have accidentally unplugged by one of them, and they plugged it back in.
Are you sure it is not the "ABS" light? That would be the anti-lock brake sensors, and they could easily have been goofed up. I would believe they could mess up the ABS light more than the airbag sensor.
If the shop does other repair work, they should be able to check it out if you tell them it came on after they worked on it. They will probably be as baffled as you are. Maybe the negative cables need to be disconnected off of the batteries to clear a memory code.
Playing with the wiring or boxes is not recommended as an accidental airbag deployment is $$$$$.