Well, they weren’t claiming a medical diagnosis. They were evaluating his potential performance in court based on how he managed his interrogation.
The quote is hardly ever given in its entirety:
“We have also considered that, at trial, Mr. Biden would likely present himself to a jury, as he did during our interview of him, as a sympathetic, well-meaning, elderly man with a poor memory,”
Hur was not diagnosing him, he was saying how Biden would present himself to a jury. Those are two different things.
This story is intentionally being distorted.