This is absolutely a thing they do at the tech company I work at too. There's hard limits on how many people can be rated anything 4 stars and up. Managers have to go to "calibration meetings" where they argue, in front of HR, with other managers about why their employee deserves one of the spots in the 4 (or more) stars club.
Right, they use a bell curve. Which means someone has to get a poor rating, even if everyone was exceptional. It's BS and should be illegal.
Performance management systems have always been rigged. Certainly at the last company that both my wife and I worked for. She had to manage a small staff, and come review time, she rated one deserving employee with a 4 out of 5 overall. HR called her in and said, "You can't give anyone a four, we don't do that here." They changed the scores and the employee got a 3 like everyone else. Complete bullshit.
