The only issue I see is how the test bank was procured. Many publishers do make test banks available and others do not. If an IM was attained through theft or deceit, then clearly it posed an unfair advantage to those who used it, and that of course is cheating. Considering the multiple Universities, publishers etc. that he contacted prior to even giving this lecture, I'd say it's pretty clear that the test bank was not public domain. Remember, it was another STUDENT in the course that turned the cheaters in, so it was obviously not a kosher practice.
As far as everyone calling this prof. lazy for using a test bank, perhaps you should ask a University Professor what they do with all their "spare time." New prepping a 200 question exam several times per term is an massive undertaking especially if you are trying to write a fair exam that's relevant to the material covered. Moreover, for all we know this is but one of several classes he is responsible for teaching, so if he uses banked questions that are supposedly secure, I don't blame him one bit.
Sure it sucks for those who didn't cheat, but given that he could have just let 200 people get booted, I think he was more than fair. He is responsible for the integrity of the course and I believe he defended it quite well.