Flashing airbag lights and other odd electrical behavior (random wipers, perhaps your non-working horn) are often warnings of a dying battery. Perhaps your battery is old and they left the door open or hood (if you have a hood light) open for a long time with the battery connected and discharged it enough to push your battery into limbo status.
I've never seen it myself but the "flashing airbag light for no apparent reason" in the past in these forums has usually been followed by a dead battery, or fixed with a battery replacement.
I had 5 batteries in my car over 9.5 years, I think the car's electrical system is just inherently unkind to battery life.
my 2c,
-Peter
04 Mazda 6s V6 MTX, in service 10/28/03

02 Subaru Impreza Outback Sport 165HP 4cyl auto AWD
former: 95 Mystique LS V6 MTX [11/14/94-5/19/04]