The author does not make a claim that credentials are stored in the clear. The author only says that he cannot think of a good reason for the limitation and ask

The author does not make a claim that credentials are stored in the clear. The author only says that he cannot think of a good reason for the limitation and asks for help from readers in explaining why this limitation exists. He says that the only reasons he can think of are similar to storing passwords in plaintext, but makes no claim that these are the actual reasons.