I had not heard this JFK conspiracy either, but here is more on it:

https://www.nbcnews.com/news/other/a...un-f2D11634276

Sounds like it was a book called "Mortal Error" that started this one.
https://en.wikipedia.org/wiki/Mortal_Error


Then of course, another one "shooting holes" in this theory
http://www.philly.com/philly/news/Sh...t_Kennedy.html