I can’t seem to see any relation between the two scripts.
The TCP/IP Predictable TCP Initial Sequence Number Vulnerability script checks for the values that are set in the Nmap (NASL wrapper) script. It might occur that the checks are somehow reacting to the configuration of the telnet port, but other than that they don’t belong together. Since the latter script is basing its checks on the NMAP output, I guess one could say that any open port is being checked here.
There is no relation between the Telnet Unencrypted Cleartext Login and TCP/IP Predictable TCP Initial Sequence Number Vulnerability VTs. But still the following plays a central role here:
This VT has a dependency to Nmap (NASL wrapper) which is a port scanning VT. If you add the TCP/IP Predictable TCP Initial Sequence Number Vulnerability VT to your existing scan config and Telnet ports are then found it means that your scan config doesn’t include this mandatory port scanning VT as already pointed out previously by @_ad: