The glitch seems to have happened because at least one ISP - Sweden's Netnod - was directing DNS requests to a root server based in China. And China automatically changes DNS routing information to redirect users of these banned sites to its own servers instead.
The China Internet Network Information Center (CINIC) says it had nothing to do with the redirection.
"As the local host of the mirror site of I root server which was agreed by I root server administrator, and also as the '.cn' registry which is one of the members of DNS community, we wanna clarify that CNNIC never did any interceptions," wrote Xiaodong Lee on a DNS email forum.