As someone with firsthand experience in writing tests, I can't actually blame him for using the publisher's test bank questions -- writing good test items is hard! On the other hand, in the video linked in the article, he never actually claims to have written the questions. He only says that he "creates" the exams (though, granted, his phrasing is a little misleading). Again, as someone who's written exams before, I think creating an exam based on a publisher's bank of questions is a legitimate way of writing an exam.
As usual, I suspect the real truth of the matter is quite a bit murkier than is being presented by either side.
 Test banks and solutions manuals are frequently only made available to professors, so if the materials were obtained by pretending to be a professor, I'd definitely consider that cheating.