The article says determining filetype via heuristics is better than via extension. I don't agree with that, heuristics are confusing. File extensions lead to behavior that a human can predict.
mv image.png program.exe mv program.exe sound.mp3 mv sound.mp3 text.pdf Same file, always a PNG despite the extensions I can attach to it.
In Windows extensions have a meaning. In Linux, why even bother having extensions? In neither OS does the extension tell you about the content of the file. But on Windows the extension does tell you something useful about how the OS interacts with the file.