The question is how do you train your LLMs to not 'cheat'?
Imagine you have an exam coming up, and the set of questions leaks - how do you prepare for the exam then?
Memorizing the test problems would be obviously problematic, but maybe practicing the problems that appear on the exam would be less so, or just giving extra attention to the topics that will come up would be even less like cheating.
The more honest approach you choose, the more indicative your training would be of exam results but everybody decides how much cheating they allow for themselves, which makes it a test of the honesty not the skill of the student.