I think you're right, and that test prep materials were included in the dataset, even if only by accident. Except that humans have access to the same test prep materials, and they fail these exams all the time. The prep materials are just that, preparatory. They're representative of the test questions, but actual test has different passages to read and different questions. On to of that, the LSAT isn't a math test with formulas where you just substitute different numbers in. Which is to say, the study guides are good practice but passing the test on top of that represents having a good command of the English language and an understanding of the subject materials.

It's not the same as the Nvidia driver having code that says "if benchmark, cheat and don't render anything behind you because no one's looking".