A small game or a little idea could became something bigger.
You did a good job, and I was thinking some things you can improve:
Instead of 4 buttons you can use 16 buttons with the number as image, and a variable to keep where is the hole. If you click at +/-1 from hole (x or y) move button and refresh hole location.
Also, when I play, I noticed that doesn't matter where's the empty hole at the end, but is usual to put it at the lower right corner. (maybe replacing "" with " "?)
P.S.: 2 years??? time flies