The distinction probably came from Macintosh though it was more pronounced in Windows 95 - also it is the other way around: something can be a folder but not a directory. Classic example would be the "Computer" (or "My Computer") in Windows which is a folder but not a directory. The Windows Shell maintains some sort of VFS that exposes these.

Generally a folder is a directory-like thing that groups file-like things but not necessarily mapped to real on-disk directories and files - and more often than not, it is exposed via GUIs rather than command line applications. Of course that is just common use not anything inherent - after all on Linux it is common to expose stuff via the filesystem (sometimes in addition to VFSs) that still uses the terms directories instead of folders with the only difference for when one is used or the other to be if it is done via a command line application or a GUI application.