To summarize the link above, it's these lines in sshd_config that does the magic.Match User sftpuser ForceCommand internal-sftp <snip>
The first line will tell sshd what user(s) the rest of the settings apply to.
The second line tells it to go straight into sftp mode. So this will only apply to the users that match the rule above.
Just make sure to test SSH after you do the changes ok a new session otherwise you might just have broken SSH access.