The distance from Wuhan of the discovery site of RaTG13 is irrelevant, if (as the article implies) a senior team at the Wuhan lab were working on RaTG13.
The article is not suggesting that Covid19 evolved from RaTG13; it is suggesting that Covid19 is a chimaera made with RaTG13.
The NYT is a reputable organ, known for checking it's sources. Unlike Wikipedia, newspapers don't generally cite their sources; but if a reliable source states something like that as fact, they've probably checked. You're right: they haven't said they can prove it.
[Of course, it could be propaganda, government or otherwise; or it could be a damned lie concocted by the reporter or editor. They've said they have sources, they haven't named them, so it's not unreasonable to suppose they have sources that don't want to be named.]
The article is not suggesting that Covid19 evolved from RaTG13; it is suggesting that Covid19 is a chimaera made with RaTG13.