In this case, that's because he's got rid of his Linkedin account since that article footer was written (I follow Neil via Mastodon, he discussed it there).
If the blog footer is intended to contain links to identity, I'd make that whole footer dynamic and then I'd just keep a single source for that.
Alternatively, arguably better: Keep a master domain for each identity and update social media accounts for that identity on a page in the master domain.
(edited for missing word!)