Yes, basically that's correct
But it makes sense to copy everything into a new FOLDER on the external drive, so you don't end up with the loose system files lying about on the external drive that can go missing or get mixed up with other things.
You can make as many backups as you like and even partial ones, just give each folder a name like
"2012_09_24 Full Start55 backup" or
"2021_09_24 Start55 North America v895 map only"
Having at least two backups can be a god-send at times.
e.g. backup as soon as you've done a major update, then make another backup just BEFORE you do the next one. That way if there's any problem with the device you can re-load the newest backup, but if there's any problem with the new software, you can really easily revert back to the previous one.
Backups made with HOME don't let you do that....
The whole process should be made clear in those instructions I inked to. If anything isn't clear, can you let us know so we can improve it?