There are plenty of good managers mixed with the bad. Obviously you knew your boss in this case was a good manager and trusted him with that info. Hopefully people realize when to trust the people getting the feedback and when not to. Generally when exit interview feedback starts to look the same from specific departments or managers...the upper ups and HR take notice that something is off. I've also seen feedback from exit interviews that people aren't happy about stuff that they knew was part of the job (like left before and came back and were somehow surprised the job was the same).