Codeigniter vendor folder use

The vendor/ directory is a Composer thing. If you've used composer before, you'll know what to do with it, but for CI in particular, you just need to specify in index.php the location of the system/ dir.

But anyway, that's not why I'm replying ... the only official CI repository for composer is codeigniter/framework. What you've used is made by a random user and is outdated and insecure.