Ford strikes again
What it's doing is regenerating the particulate filter, at idle.
What they do is dump extra fuel into the cylinders on the exhaust stroke. It doesn't add any power but it dumps raw fuel down the exhaust where the hot catalytic converter ignites it and it burns the particulates out of the filter.
All the new diesels do it but the Dodges do it at highway speeds only, not at idle. You notice the guy revs it up and it clears out but if the video was longer you'd see it light off again as it idles.
A simple software change will correct this but how in the world did Ford overlook this? To me it's just representative of their engineering.