We could definitely add a test for this. However, it becomes unproductive (see impossible) to write test cases testing negatives for actions Campers could take.
What I mean by that is, we could also write a test you do not write the word “hippopotamus” in the code anywhere, because the instructions do not ask you to. Whilst facetious, we do prefer to be more lenient on the tests passing, rather than causing potentially correct solutions to not pass, or confusion.
So, I think we are better going with the change you suggested to the instructions wording.