Of course slip-ups happen, but then it should have involved more people, and should not have left this impression on the ex-employee, but rather the impression

Of course slip-ups happen, but then it should have involved more people, and should not have left this impression on the ex-employee, but rather the impression that HR didn't have his back (but at least were there as a second pair of eyes in the process). This sounds more like no oversight at all. Sure, we could be missing something.