The bug is definitely in your game as it hasn't happened before or since without the game running. And, as a Mac user, you can appreciate the unlikely power of a bug that can freeze the entire system. I couldn't even move between windows. I don't think I was even doing anything particularly heavy with the computer otherwise.
If I'm the only one then it might be a freaky me-specific issue. Hope so!
I admire your game! I showed it to other game designers as an ideal of the 'game is analog but wouldn't ever actually be fun playing analog.'