They are not hotlinking ghost urls... JSdelivr is a giant JS CDN. Ghost is in the url because they developed the library so it's the GitHub path. You could use this library on your website right now... They open sourced it!
The asset that thefp.com is using is the one that gets loaded from the latter (the one served from the public CDN), and you can see that this was true even at the time that O'Nolan's screenshots were taken. For some reason, he mixed them up; the only evidence that we have of anyone here using the CDN that Ghost is (presumably) paying for is Ghost's own use of it themselves.