If you do not have an active Duo account, please for your UNI. Telnet is just they way they have device access set up. However, telnet is also useful for things other than access cli on devices. Its a great troubleshooting tool to see if a server is responding, such as running 'telnet 1.1.1.1 25' to check if a mail server is actually responding for example It has a network diagram, you click on the device and it tries to launch telnet://x.x.x.x in terminal.
