The authors misunderstand git
> there is a lot more duplication of code that happens in GitHub that does
> not go through the fork mechanism, and instead, goes in via copy and paste of files
> and even entire libraries”
At face value they appear to have checked the GitHub repository being marked as a fork. But it is quite easy to fork without it showing in GitHub. Given the basic model of submitting a pull request is to start with a fork either in GitHub or by using a local repository there will be a lot more forks than immediately shows.
Why would anyone go through the local route: interested in how it works so clone locally. Make a change and then realise I want to push that before creating a PR. Given changes already committed the new remote approach is easier.
 Clone GitHub repository to local; create new GitHub repository; set new GitHub as remote in local repository, push local to new remote.