In Linux based operating system everything is a file. Directories are special kind files.
Linux Is Case Sensitive: Linux is case sensitive which means these files filename & Filename would be counted as two different files not one due to difference of f and F and thats why /home/filename is different from /home/filename.
Here file utility determines the file type. Linux don’t care extensions to determine file type. It don’t care weather the file ends with the extension .odt or .txt System administrators use the file command to determine the file type.