I asked that npc too and I didn't have the paitent to play. But i guess you have to win him multiple times to gain the reward
So I've beaten the GOG monk in the Flotsam tavern (basement level) and was greeted by an addition to the tutorial part of the game instructing that I should look into the Extras section of the main menu to learn how to get my reward...
Problem is, there's nothing in the Extras section except for the Credits. So what happens now?
Nice little Easter egg though.