Major enterprise vulnerability scanner author here (15 years ago). Yes, we scanned the port, and yes, we ran a lot of fingerprinting rules against it until we figured out what it was (or ran out of rules), so that we'd know what vulnerabilities to test for.

This had some amusing side effects when we encountered some services we'd never seen before, like the port on HP printers that sends every byte straight to print... apparently expecting PCL or PostScript but if it didn't understand it, it just printed the ASCII. Came into the office one morning to find all printers out of paper and 500 sheets sitting in the output tray. Oops.