Hi chong!
The digits DO correspond to Pi... written in hexadecimal base :D. That means Base-16, or in other words, the numbers go 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, a, b, c, d, e, f, and only then you reach 10. In this system Pi is written as:
3.243F...
which is exactly what you get in the game if you start from the 0-th digit. The reason for this choice is that base 16 allowed for a nice 4x4 grid, while base 10 would have not. I could have done it with a grid of triangles but that would have been more complicated and I really made this in a hurry!