Nmap gets port names from IANA, with some community input for very common services. Port 9103 is frequently used by JetDirect printers, which is why it is labeled that way. Use -sV to probe the target and identify the service itself. Unidentified services can be submitted directly to the Nmap Project: https://nmap.org/book/vscan-community.html
This is a better topic to discuss with Nmap development community, not the Debian package maintainers. Please open an issue on http://issues.nmap.org/ or join the Nmap developers mailing list: https://seclists.org/nmap-dev/ Dan
