From looking at other modules and such, it seems that the OptPath is used for sending files from Metasploit into the module, such as when brute forcing logins and the OptPath points to the passwords.  In this scenario, the FILEPATH is the file that will be returned by the web server. 

As far as I can tell, I think OptString is correct. Please let me know if this is incorrect, I'd be happy to adjust it.