My agree might be premature, because I've never actually read the bylaws or the memo.
But based on legal principles I'd like to present what I think would be the analogy. In law, you have a statute and then regulations which draw jurisdiction, or permission from the statute. If the statute says, for example "the regulations may define x", and the regulations attempt to define y, then those regulations have exceeded their jurisdiction and are ultra vires and therefore of no force or effect.
So if the NFL bylaws say the commissioner may describe the colour of the clouds, and Goodell says in a memo that the sky is green, he's acting beyond the powers of his enabling bylaws, or acting contrary to them. And if he's wrong in interpreting or applying the bylaws, no one is supposed to be bound by his mistake.
So if my analogy is correct, and I'm going to assume a memo is akin to regulations, that is Goodell as regulator interpretating the enabling bylaws, then Arch is probably right. And I wouldn't trust that moron with a communications degree to interpret anything either.