I don't really know, I mean they might even be using SFML - because the game runs exactly the same except for some UI tweaks. The thing is I was the developer of the project for more than 4 years and I was burnout didn't want to add more features just wanted to release it already but it didn't happen so I kind of left the team (which was just me and another by the time).
Shortly after that the game was released under a publisher.
Anyway I am thinking of start something small soon, to get back to gamedev. I've worked on a game studio for a few years using Unity and it's very nice because of the easy portability but kind of meh and adds a lot of overhead, dlls etc. I'll probably check out SFML again, the last version I used was 1.6 lol!