They are not, since the author had no creative input into making the games. They are technically "fanfiction", however CDPR did such an incredible job I think they're actually much better than the books and should be held in higher regard than your typical fan work. I've read all the witcher books and played all the games, and I'm also a big fantasy novel fan, to me the books are only average, with the exception of the first 2 short story collections, while the games are some of the best forms of entertainment ever created.