Is sshd really not part of systemd?
Yes, it's not a part of systemd. By running systemctl restart sshd
you are just restarting the sshd systemd service. Systemd service files for things like ssh and transmission come with their respective packages.
You can see what I mean here. The openssh-server
package for Ubuntu comes with the sshd.service
file.
You can change the update notification frequency somewhere in settings. Pretty sure you can disable it too.