According to the Wiki article, it is left ambiguous whether there is magic and it could just be perceived to be that by the characters. The laws of nature changing spontaneously to make some types of technology impossible is in itself not supernatural (although it could be, depending on the cause).
That's not to say that the classification has any impact on whether the books are good or not, of course. But it doesn't read like an example of fantasy where technology doesn't work.