Where did you get the idea from and when?
me and my close friend started this jam for fun about 75 days and this is our 5th one! heres the first if you wanna check it out. https://itch.io/jam/pb-and-game-jam. hope that answers you're questions :)
each jam starting from this one we have tried to try different little ideas to keep are jam unique as most jams stick to one unique idea we change it every jam! so i thought of two themes or one theme at the beginning of the week and then the theme switches to a different theme but the second one felt confusing to me so we stuck with two themes for this one. as well i searched on google game jams with two themes and I saw that there was a result that said "Ludum Dare 34 game jam will feature two themes this time" and i thought that was cool that it was the same idea. hope that answers you're question again :)