Why wouldn't the company discuss internal staffing?
If a manager is trying to fill a position and got a candidate from another department, one of the first things that they're likely to do is to ask the candidate's current manager what their view is of the candidate. They're going to have a far better understanding of the person than you can get from an hour ...
Do what you need to do to survive in this workplace
Look for new position and leave as soon as you find one
Given this manager is certainty been in the company longer than you, higher guys like his results and ok with his style of management
Am I unreasonable to expect that internal job searches at a very large company should be kept confidential between the hiring department and the internal applicant, at least until a hiring decision is made?
Probably, yeah. And why should you want that, anyway?
Look at what has happened. It sounds like your manager is startled to learn that you're unhappy ...