This article doesn't do a great job of explaining the situation. Essentially Iceland signed a treaty that allows them the benefits of participating in the EU's

This article doesn't do a great job of explaining the situation. Essentially Iceland signed a treaty that allows them the benefits of participating in the EU's markets while not requiring them to join the EU. As part of that treaty they are required to guarantee the savings accounts in Icelandic bank up to around $30,000 (In the same way FDIC guarantees accounts in U.S. Banks). When Iceland had their financial crisis the government decided to guarantee the accounts of its own citizens but not those of foreign citizens who had accounts there. Which is in direct violation of the treaty. This vote was the people of Iceland saying they don't care what their obligation under the treaty is they aren't going to pay.