File extensions are more nomenclature than file type indicator. More than one file type might share the same extension, more than one application might be used to open the file according to its extension. They mostly work, but file extensions != file types != file creators.
File extensions are trivial to fake, don’t really have a strong association with the application that is supposed to handle them, and in this case often doesn’t even apply because most of the files in my home directory seem to lack an extension.
Isn't what you describe basically the file extension? Not so much what program created the file, so much as what program is meant to handle/open the file.