By default, telnet is enabled to be access by remote logins for a non-root user. To allow a root user to access the telnet remotely you will have to explicitly allow it.
This can be done by commenting the following line in the file /etc/default/login:
But please understand the security threat behind this, first telnet is insecure and hence is not suggested method of remote access, instead use SSH. Besides allowing remote login for root via telnet is a big NO NO.
You’ve been warned!