As you can see in this Reddit post. The game probably counts draws as won games. I don't know if Coven games are included in the end-game graphs but if they are this achievement (and also probably all the achievements which is awarded by winning games) are bugged. As you can see in the images I have 98 Wins, 60 Loses and 2 Draws but I still got the "Zealous" achievement which is awarded to players with 100 Won games.
Images to prove
The end-game graph with 98 Wins and 2 Draws
Yet I still got the "Zealous" achievement