The 'SFTP' page describes only how to access your sme server and do file transfers over SSH, and has no relationship at all to FTP.
While this works, the last time I checked (admittedly over a year ago) there was no 'chroot' capability in the SME ssh server - so if you set it up, all users need to have shell access to your server, and will then have access to all parts of the system that have the 'other' access right set to 'r'.
There is a separate file transfer capability referred to as
FTPS that involves using the legacy FTP protocol over an SSL encrypted connection. I don't think that SME server supports this protocol (see
Bug 644).