If a test in no way distinguishes between knowledge gained by different methods it has no right to call one method 'cheating', no matter what it may claim.

Surely by that argument there is no such thing as cheating. If I gained the knowledge necessary to pass the test by brekaing into the headmaster’s office and taking a photocopy of the questions and their answers before the exam, by your criterion that isn’t cheating.

I would agree that the wording is not robust against hostile interpretation, but not much more than that. While "breaking into the headmaster's office and stealing the questions and answers" and "reading the English translation of a book" are both methods of gaining "knowledge" most people would consider the kind of 'knowledge' gained to be sufficiently different that they would not equivocate between the two.