I guess that would be that famous Icelandic dry wit of their’s.
The official Icelandair store sells “A VOLCANIC POSTCARD” for eur 6.
A postcard with a tiny sample of real volcanic ash from Eyjafjalljökull and a great picture of the eruption in 2010. Send your loved ones or your friends a piece of Iceland.
I guess it must be part of their “this is why you are stuck in the airport” range.