I wonder how much of this is a result of lawsuit culture. For example, American companies won't tell job applicants why they get rejected, lest they get sued by the rejected candidates. And perhaps this has carried into feedback for actual employees. It sounds like the author wasn't even he was on a performance improvement plan, he had to infer it and pull it out of his manager.
Is this the general state of things in the US? In the same way people are afraid to say their (non-racist) opinions on Twitter due to groupthink and getting hit by mobs, are companies now taking this approach with their employees out of fear of being sued?