Clearcase stores its 'files' as directories
What Aric is trying to tell you is that ClearCase uses extended path names, "extended" because it extends the file name with version path.
So in a dynamic view, any file can be described to reveal its versioning path:
$ ct ls
myFile
$ ct descr -l myFile
myFile@@/main/3
In a dynamic view, you can actually explore the versions of a file (hence the "file as directories") part
$ cd myFile@@
$ ls
main
$ cd main
$ ls
3
$ cat 3
... // content of third version of myFile
Now, if ClearQuest (the issue tracking system) were used here, it would reference activities (change set of file set) of ClearCase.
But with ClearCase, a version of a file (referenced by ClearQuest or obtained through another mean) can very well has been deleted in the dynamic view ("rmnamed" actually).
Meaning a file may be referenced by ClearQuest or by some ClearCase activity, but not be visible directly with ClearCase in the dynamic view.
However, its extended path name would still be accessible in that same dynamic view.