They are talking about the crown of the root mass. If you are concerned that you may be burying it too deep. Then wash away some of the dirt at the base of the plant. Look for the point(CROWN) that's where all of those fiborus roots meet and where the new shoots come from. Measure from there and bury. Good luck Gianty.

Nixon..
I think you understand correctly..when you see a clematis in the pot..up the stem you'll see the first leaf axil..Make sure that is buried undergroud...This will give you several nodes that will root and send up new stems which = more vines. I always plant mine at a slight angle towards what I want it to grow onto....Jeanne

Thanks for the clarification!

Yes, you should plant them deeper than they are in the nursery pot. You understand correctly. Burying 3-5" of the stems is what you want to do.