a little clarification about contextual filter
1) Content refers to Node in Views 3.x

2) Contextual filters are filters. That means that any filter you add here is a dynamic filter fetched from context (page path arguments, node data etc). So they are filtering all the results (views data if you prefer it).

A good idea is to enable the display of the database queries (admin/structure/views/settings) so you can inspect what are you doing with every views settings.