There is no original name.

print "this is perl.\n";
[download]

That's a snippet that even I have no name for, so the engine does not know what to name it. But it is downloadable. The fact that it's called "index.pl" is because that's the file that was called (perlmonks.org/index.pl)

Note: Some browsers (Mozilla) will display the code and not present you with a Save dialog box.