How to find and access "device folder" using PC?
What You see is output of libmtp (Media transfer protocol) and appropriate plugins for file-manager. To access root directory of Android device from Linux, you might use 

a) adb shell (using terminal - easy solution)
b) several mtp packages listed nicely here

steps described in b) should allow You to mount root of Android device and access it from file manager, however it requires some non-trivial system modifications.