As far as I know, including a reference is required, but the way you go about adding it is pretty much irrelevant. It's highly unlikely that you get disqualified so long as you, like, put a pie literally anywhere in your game or append "and [Emoji]" to the end of some npc's name, or just have something mentioning any of the museum entries somewhere in the game, no matter how shoehorned and out of the way it is. The reference can just be thought of like an easter egg that's really not relevant to the game as a whole, and it can be as tiny as you want. Unlike the theme, it's also not a rating category, so you will not be judged if your implementation is shitty, and I believe you get to explain in what way you added the reference when submitting.