> The benefit of explanations in tests is...

What you appear to have in mind here is the documentation of a test. Any documentation that correctly explains why it matters that the test should pass will likely tell you something about what the purpose of the unit is, how it is supposed to work, or what preconditions must be satisfied in order for it to work correctly, but the first bullet point in the article seems to be making a much stronger claim than that.

The observation that both tests and documentation may fail to explain their subject sheds no light on the question of whether (or to what extent) tests in themselves can explain the things they test.