No they didn’t prove that. To prove that they would have to dig up Thomas Jefferson. The story itself was defense of Bill Clinton done by the British journal Nature. It was such wild speculation that the American journal Science immediately came out with a rebuke of the journal Nature.
Exactly. What little I know of DNA, the only way to be sure is to have direct relations compared…parent and offspring. There is no way 200 years on we have access to compare anything truly relevant.