The new part of this article is the physical letters that were sent to some of t...

The new part of this article is the physical letters that were sent to some of the people mentioned in the tweet. That hadn't happened when the previously-discussed article was written.

(Edited to add: However, an article discussed yesterday in a now-flagged discussion did have the letters: https://news.ycombinator.com/item?id=39199703 )