So my friends in a small game dev group I'm in thought we should all do this jam. I decided to join as a solo developer and to see how well I'll do compared to them.

They brought up the fact that the theme is optional (I was always under the impression that it was a must) So is the theme for bonus points? If not: I might not use the theme in the end.

well it says it's optional if you want to follow the theme if not just mention it in you're game

Yep, the theme is optional. The only disadvantage is that you may not score as well in the THEME category. However you can score well in the other categories as well as the overall category and you'll be fine. Don't let the theme discourage you from making a game idea. I'm pretty sure this years theme for the jam will be pretty open :)