No, you haven't misunderstood.
What I was referring to was the ability to do it all offline.
Currently, with Wahoo, you can create the route offline but to import it into the app you do need an internet connection, either data or wifi.
The advantage of using a cable to transfer the file to the unit is that no internet connection is required as the app is bypassed.
Of course, if you have an internet connection, you can use the "Take me to" functionality of the app, no need to go an external planner.
It is about the only advantage the Garmin has over the Wahoo units, in my (admittedly Garmin unfriendly opinion).
And it really only applies to those touring in places where internet connectivity is an issue.