I don’t know what is a big or a small stretch. I just know it is just not true. If you studied the history of the second World War, or the history of the CIA, or the history of the Cold War then that sentence sticks out like a sore thumb. It makes as much sense as describing how many Gatling guns Hannibal mounted per elephant.
I guess in a certain post-truth sense it is a smaller stretch of the truth to say that the CIA published it, than to say that the KGB did it. And in turn attributing it to the KGB would be a smaller stretch of the truth, than attributing it to the elves of Middle Earth. But what is common between all those three is that they haven’t authored this document, because it was the OSS who did it. (As the document itself conveniently, and very prominently states.)