Literally, it is fiction made by fans, after all. The developers have repeatedly mentioned their admiration for Sapkowski's work, and demonstrate that admiration with the details they include in their games. There are terms which need not always be pejorative in all contexts, and I think this is one of them. It may be an over-simplification of their achievement as game-designers to call it 'fan fiction', but the description, if unflattering and a bit deflating, seems accurate. In any event, it does look a far sight better than your average fan fiction, and I think most of us here are profoundly impressed with the company's work. However, would CD Projekt Red have succeeded without Sapkowski's writings, from which to draw inspiration?