From the Github description, a quote: "In a class I taught at Berkeley, I did an experiment where I wrote a simple little program that would let people type either “f” or “d” and would predict which key they were going to push next. It’s actually very easy to write a program that will make the right prediction about 70% of the time. Most people don’t really know how to type randomly. They’ll have too many alternations and so on. There will be all sorts of patterns, so you just have to build some sort of probabilistic model. Even a very crude one will do well. I couldn’t even beat my own program, knowing exactly how it worked. I challenged people to try this and the program was getting between 70% and 80% prediction rates. Then, we found one student that the program predicted exactly 50% of the time. We asked him what his secret was and he responded that he “just used his free will.”"

I can get it to about 60%. Given the algorithm used, it seems like it should be trivial to "trick" it by just cycling through novel 5-grams over and over, but to be honest I can't be bothered to check. And that would be rather contrary to the point of the exercise, if somewhat undercutting of the premise that free will is equivalent or comparable to randomness.