Telnetd sensor node what?!
I call it a sensor node (more on that in a later post), you might call it a telnetd stub. We are essentially talking about a telnet service which looks like a telnet service, is fingerprinted as a telnet service, replies like a telnet service, but is limited to bare minimal functionality and just meant as a sensor to gather information.
In this case, we are looking for the folks who are looking for us - or, who are looking for exposed services on the interwebs (or maybe your corp network?).