I don't think that's true.
You can get injuries from over-use, even if you do everything perfectly. You can develop some sort of imbalance through other activities that could lead to impingement and injury, even if your bench was perfect. The structure of your shoulder may be such that impingement just happens very easily. And it's known that some people just have inherently much weaker connective tissue, almost certainly for genetic reasons.
So that is at least three reasons why you could have totally flawless technique and still have lots of shoulder injuries.
It's comforting to think that all you need to protect yourself from injury is good technique... But it's just not true