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.
> Classic example would be the "Computer" (or "My Computer") in Windows which is a folder but not a directory
This sounds backwards to me, going by the real life counterparts for these terms. A directory is a list of pointers to items located anywhere (eg. a phone directory for a business may contain corporate and other remote numbers alongside local extensions), but a folder contains actual files that are physically located inside it; you can put references to remote items inside, but only by placing a physical representation/reference inside of it.
I was first introduced to "directory" as a type of signage at malls or clusters of shops, listing where things are. Usually also having a map, with a red triangle labeled "You are here.". Then I learned that telephone books could also be called be called directories.
My first exposure to computers that had a file hierarchy used the term "folder". When I eventually encountered "directory" in computer usage, I was confused because I thought first of signage in malls.
It still "feels wrong", so I usually use "folder". (-: