I see, and I feel the same. The jam page also states that you won't get disqualified for not adhering to the theme, which for me signals that Mark thinks the same. It's meant as a starting point for inspiration, not as a checkbox you have to tick.
One of the best jam games I've made had it's main mechanic discovered during prototyping, even so I'm still very focus on wanting a complete idea before I write a single line of code. In this jam, at hour 38 or so I still hadn't gotten an idea I wanted to make, but I felt like I just had to make something so I started with one of the ideas.
This turned into spending 4 hours making an 3D elevator, but then figuring out that I wanted a 3D puzzle on each floor. After brainstorming 3D puzzle design for 3 hours I finally got an idea I wanted to make, and the elevator got scrapped entirely (even if it's still in the game files haha)