why would the airbags deploy if not in an accident,cars been sitting for awhile?

When airbags first came out there was a sticker saying after 10 years the air bag system needed to be inspected and if a customer insisted on an inspection I was told for liability purposes the dealers were to recommend replacing the air bags, It is rare for them to falsely deploy unless some one has disconnected the yellow air bag harness with the key on or the module receives and erroneous signal to deploy the air bags.

I agree with Greg, it is likely due to their age. It is rare that this happens. I recall road testing a Ford Ranger that had been in an accident and repaired a few months prior. The bags did not deploy in the accident, but while we were driving it, one of them deployed. No other issues, just a failed airbag.