Yeah, that is a little confusing. Basically, the 10 and 20 foot cords should have had the inline choke (puck) thing built in. It isn't. So instead, humminbird added two shorter cables to add the end of each interlink connection. That choke or "puck" suppresses high frequency noise from entering your locator.
In theory, if your interlink is right next to your locator, you could connect one end of the short interlink "puck" cable to the interlink and plug the other end into your locator and not need to use both of the longer wires.