I am pretty sure like 99 %. Here is why. Firstly, looking at company strategy for year 2013 and years 2014-2016 (game production) published in 21 march 2013, we can see that the board game was actually planned for year 2013. Later on it was pushed till 2014. IIN strategy for years 2014-16 there are 4 different project listed as follows:
- Witcher 3
-Cyberpunk 2077
- 2 smaller (gameplay time approximately 20 hours long) top quality projects supporting one of main production lines
- cross-platform game for mobile devices based on one of our brands
As you can see, these 2 smaller project are listed separately from mobile game. Board game is listed in previous year.
Secondly, if you study job offers you can sometimes predict what people are doing and where. For example, CD project REd were looking for producer specialised in mobile games for a position in Warsaw. So, it is most likely that mobile game was being developed in Warsaw (board game version, maybe CD projekt part of Moba game). We know from Adam KIciński that one of these smaller projects is being developed in Krakow (starting in july 2013). I am not sure about the other one. If you look at job offers in Krakow, you can see a position of a writer is open. Writer writes dialogs, design plots and so on. You don't need one for mobile game. Also, the job require extensive knowledge of Sapkowski books which says to me that they are working on witcher product. My guess is (educated one) that Krakow studio develops Witcher 3 paid expansions offering 15-20 hours of gameplay each.