The top right search box will search all files in a specified location. The top left search box does the directory search but it's more like navigation. The search you're asking about doesn't do recursive searches it's displaying the directory you're in and you can type out the directory within the directory you're in to access it
Another thing this does is display the path to the directory you're in. For example:
are always assumed as the user cannot ascend above
You're right, about that documentation, it is the wrong search box. The box you're referencing isn't present, I apologize.