Codeigniter download install web vs Composer

Your first link refers to a manual install. Everything gets expanded into the folder you extract into.
The second install link refers to a composer install. Composer is a PHP dependency manager, and it automatically pulls in any external packages, putting them all into the "vendor" folder. That is "normal".

Your manual install has a composer.json file in it, defining the dependencies. If you run "composer update" inside the folder, you will end up with the same "vendor" subfolder as with the composer install.

The vendor folder contains the external packages needed to run unit testing for the framework files.

"bcit-ci/framework" has been replaced with "codeigniter/framework". If you look at the entry on packagist.org, you will see "This package is abandoned and no longer maintained. The author suggests using the codeigniter/framework package instead. "