In the same way ChatGPT scores 25% on this and the question is "How close were those 25% to questions in the training set". Or to put it another way we want to answer the question "Is ChatGPT getting better at applying it's reasoning to out-of-set problems or is it pulling more data into it's training set". Or "Is the test leaking into the training".
Maybe the whole question is academic and it doesn't matter, we solve the entire problem by pulling all human knowledge into the training set and that's a massive benefit. But maybe it implies a limit to how far it can push human knowledge forward.