Just to note the ‘dual screen’ thing (I’ve not read your links yet) may refer to the fact that from iOS13 you will be able to look at one app on your phone (your passenger, obviously!) and something else on the dash screen. Presently, if you have Music on the dash and open Waze on the phone, both screens will Display Waze. I think that’s what is meant by dual screen support.
EDIT...
Second video stream support
Automakers can develop CarPlay systems that show information in a second screen, such as in a cluster or HUD.