There is no option to stop the ssh server and as long as you do not open its port on your router, there is no issue.
Please to read the help page for each menu, for example you would read this for the the SSH setup menu:
You can choose two modes of identification with the SSH server of the NAS:
· SSH access by password
· SSH access with RSA key
The first mode is the default mode. Because it is less secure, it must be used only in LAN and port 22 should not be forwarded to the router table of the Internet Box (ISP box). This mode is enough to make standard actions by the administrator.
The second mode is used if you have a remote access to the NAS or you execute advanced actions (tunneling, rsync for backup, etc.) where an exchange of keys is required or best.
The firmware sends no data on the WAN, it only requests to get information from our site about firmware version and addons.
I detected you use Chrome with your activity on the board (where phpBB keeps during your session the user-agent information, it is a way but not the only one, to avoid a session hijacking)