Van1, the rivet failed, more than likely, in transit from Jackson Center.
If you have an awl, you'll probably be able to stick it into the hole and feel the other end.
I would be more inclined to blame the dealer for not noticing the missing rivet.
With so many, rivets DO fail in most trailers (all brands that use this method of securing). Tech support at Airstream will send you a handful.
Go to Lowes or HD, get yourself a rivet gun, and be prepared for the future. It more than likely will happen again.