I know this is a late response and I'm not an organizer of this event - but this "from scratch" rule typically means not to reuse game mechanics you've implemented before. Such as slapping in a fishing minigame that has been made way before. You should be good to reuse any "tool" based code you've written before, however realistically I've never seen anyone penalised for breaking this rule (except for people who were obviously just submitting one game to multiple jams, with very minor modifications).