Reading the JAMA link Nick gave, it looks like they think that you might be somehow taken by surprise by the Sun reappearing and instantly damaged.
Which is kind of weird as the end of totality is always easy to see coming and I must admit I have yet to hear of the Diamond Ring damaging anyone’s eyesight.
I could only imagine a problem for people whose eyes remained fully dilated (for some medical or pharmaceutically induced reasons) or who were using a telescope/binoculars during the Ring or forced themselves to keep staring after the Ring was over. Other than that, it sounds tosh to me. But, as Nick wisely says, your experience may differ*.
*Its a bit frustrating that everyone now needs to protect themselves from the wrath (legal or otherwise) of people not thinking about the potential consequences of their own actions.