HR not honoring the confidentiality of exit interview - Network Engineer Total Information Management Employee Review

I resigned because of the stressful environment and I finally got out last year. I only had the courage to do a review because I saw another review of a former employee stating the cons of the NOC team. I had the exit interview conducted by the HR and she asked what can the company do to improve, am I really sure that I am leaving etc. I told her that the environment is stressful and it is not healthy for me anymore, as far as I know this exit interview should be kept confidential. A week has gone by after the exit interview and my Manager talked to me about the workplace not being stressful and the workload is not that heavy. Sure the workload is not heavy for the ATL above ranks because they just pass the work to Senior NEs and below. I am disappointed with the HR to whom I opened up with thinking that the interview will just be between us. Shame on you HR on letting my Manager in on this. I know the mancom will not take this seriously. But, just take a look at the manpower of the NOC Team, how long is the most tenured employee besides the "Bosses"? 1 year? 2 years?