I have no evidence for the claim, but I suspect it has something to do with a campaign that I think was started by the dominating classified ads site finn.no to get rid of IE6 (http://labs.finn.no/finn-anbefaler-ie6-brukere-a-oppgradere-...).

They made a snippet that displays a red box on the page with a warning if you are using IE6 and this got picked up by a lot of other sites. As you can see from the post above, this was in February of 2009.