As far as I know, files that begin with RIFF and then binary data are Resource Interchange File Format, which are the “container” format used for WAV music files and similar binary data.
Like I said, it looks like the CFG file at that name has been overwritten with data that isn’t normally in a .cfg. I cannot see how opening it in Notepad++ could have caused that. And if you open it with Windows Notepad (notepad.exe, that came with your OS), I am sure you will see the RIFF and some of the other plaintext, and not be able to see the original CFG data.