That's not how it works. In general, it's not enough for an HR person to "write a policy" unless that HR person also happens to be head of HR (aka VP of Person

That's not how it works. In general, it's not enough for an HR person to "write a policy" unless that HR person also happens to be head of HR (aka VP of Personnel, etc.). Otherwise, the policy needs to be reviewed and approved by the C-Suite or the Board. In Twitter's case, this policy had been in place for years before the acquisition. And here specifically, Elon agreed to this when acquiring Twitter. This wasn't something they sneaked past him; it was one of the material negotiating points and was widely reported on by the media at the time. It' not just a policy; it was a contract between Elon and Twitter (and now its assigned successor, X) with the (former) employees of Twitter as its intended beneficiaries (which is what gives them standing to sue).