Selling games DRM-free doesn't necessarily mean a store should be considered a "DRM-free store" on the whole. After all, Scheme sells some games that lack DRM, but no one other than a few contrarian shills would tell you Scheme is a DRM-free store on the whole. Epic Fail Store is a similar example: many of their games can apparently be made DRM-free but not all, and none of the DRM/DRM-free aspect is advertised (to my knowledge), so it's buyer beware.
The question would then become something like "what percentage of DRM-free games does a store have to have, in order to be considered a DRM-free store on the whole?". The answer will vary depending on people's perspective and tolerance of games/aspects that are DRMed. One thing I did want to point out is that GOG's "sister site", FCKDRM.com, features stores/sources of media that are "100% DRM-free".
Due to the existence of GWENT and other forms of what is essentially multiplayer DRM, we can conclude GOG is not a "100% DRM-free" store, though by most of our readings it is still currently a DRM-free store on the whole. That said, the more DRM or DRM-like stuff that comes here, the more that stops being true and the unique selling point evaporates.