you can connect your owncloud account on the FTP server? download data directly to their users?
You can attach ownCloud to a FTP server like explained there:
But the external storages don't pull the files to your user, it just "mounts" them into ownCloud.
so you can not upload data to owncloud from filezilla?
No, you can't. If you want to use external tools other then the ownCloud WebGUI oder Sync-Client have a look at the following FAQ for alternatives:
You need to use a client that supports webdav, not sure if filezilla does it. WinSCP does it, cyberduck, ...