Allowing an anonymous login for an FTP server is tantamount to putting up a sign which says "take the files". If you don't understand why, just follow this link. If you did, in fact, follow that link, congratulations: you just downloaded a file from an FTP server using an anonymous login. It's such an accepted thing that your web browser just did that process for you without bothering to ask if you were okay with it. You've now done the same thing he was accused of doing without even knowing you were doing it.
Putting files on a public FTP server with an anonymous login is exactly the same as putting those files on a public HTTP server without requiring user credentials. The only difference is which protocol is being used.