The article is actually a bit confusing. There was some sort of transaction involving IKEA and Ethereum. The transaction was with another company, not some random customer, though, so they might have not gone into trouble just for people. And then yes, now I got how it happened. It was a transaction that could not have happened in a different country. It was allowed because of Iceland's fiat currency being available as e-money and because it's allowed to exchange some types of digital money for others. So basically, until you have your national crypto-currency that represents your country's fiat, you probably cannot use Ethereum to pay for products you buy in IKEA.