The themes were decided by an open vote that took place on our Discord server, so the results were known and there was no way to keep it a secret. As for the jam period, we go by the honor system. There are no prizes to be won in this jam, we're all just having fun and challenging ourselves :)
Further, our rules are pretty flexible and chill. For instance, we allow the use of pre-made art assets and if you are going the homebrew route, you're allowed to get some boilerplate code up and running before the jam even starts, with the rationale that this will leave you at roughly the same starting point as someone who is using a modern engine like Godot or Unity once the jam period actually starts. This creates a fairer playing field between homebrew and games made with modern engines.