This appears to be a misquote, apparently from a conflating of Martin and Robert Jordan's old attitude (who in 1996 said he'd left orders to have his hard drive formatted five times and then smashed with a hammer if he died before WoT was finished, which obviously was an opinion he changed over the years).

What Martin has said is that there are no notes for ASoIaF another writer could work from. There's timelines, some worldbuilding notes, some unpublished maps and so on, but there's nothing someone could pick up and use to finish the series. He's also said, quite recently, that if he was similarly on the last book and was diagnosed with an illness with some years' warning, like Robert Jordan was, he would make some notes and consider allowing another writer to finish the series. If he falls under a bus tomorrow though, we're screwed. But the same is true of almost any other author writing a long-running series as well.