When nmap scans port 9100 it doesn't send anything (at least as of nmap 6.00 using -sV). It is probably a higher level vulnerability scanner, possibly metasploit, using nmap to discover open ports and then probe deeper on its own.
Nmap avoids sending to 9100 specifically to avoid sending data that the printer may misinterpret as data to be written to a page. You need to give it the --allports option.
--allports (Don't exclude any ports from version detection) .
By default, Nmap version detection skips TCP port 9100 because some
printers simply print anything sent to that port, leading to dozens
of pages of HTTP GET requests, binary SSL session requests, etc.
This behavior can be changed by modifying or removing the Exclude
directive in nmap-service-probes, or you can specify --allports to
scan all ports regardless of any Exclude directive.
