Sure, the theme is optional. You can get inspired by it or ignore it completely. I think what counts for the game to be valid is just using assets from OpenGameArt.org (and credit them).
Finally got some ideas and put them on paper. This will be my first Game Jam (and hopefully the first game project that I do from start to finish xD) and I will try to not overshoot it. I will be only loosely following the theme, but hey, I hope the game is good.