The code you posted is to have multiple wp-config.php-style wordpress configuration files with one codebase. the configuration is then based on the domain name.
imagine the localserver is listening on http://localhost.localdomain/ (no idea which one is the default with ubuntu), then the configuration file would be: /etc/wordpress/config-localhost.localdomain.php.
This is made so that the wordpress package can be upgraded w/o overwriting your own configuration. So the reason why this is done is to have an easy upgrade path with the ubuntu package manager.
I assume this does not play well with multisite, but I have no clue. It should work flawlessly with normal wordpress usage.
As Thomas MacDonald already suggested, you can always go with a manual install. I would recommend that as well because you wrote that you run performance and analyse tools and I think you want to do this on the original package. So I assume that there is no need for you to rely on the pre-made ubuntu wordpress package. That’s mainly for those who want to install it the “ubuntu way”.
Good start for you with linux, it really rocks for development. I’m sure you will enjoy it once you figured all the new things out.