The passenger side curtain and seat airbags, and belt pre-tensioner on my 2014 HSV Maloo went off while driving on a straight stretch of the Hume Highway on cruise control. The result was frightening. Holden says I ran over something, which flicked up and hit the floor and they are not responsible. Airbag techs I have spoken to say the criteria for deployment has not been met. I have asked for information of how the system works and for data from the module. They will not answer me; the whole saga is a disgrace.
I have no doubt that it was frightening and I'm equally as sure that the experts you have spoken to are correct, and that the explanation you have been given is pure fantasy. It would have to be a major side impact to trigger the bags and it would seem that just hasn't happened. Something being flicked up from the road is not going to set the bags off. Go back to Holden and demand a proper explanation.