score:2
The Wikipedia article you linked shows that the EuroCity-Express uses ETR610 trains. Since your other sources link to the seating plan for the Frecciargento ETR610 trains, I think it's fair to assume that the interior layout is the same. But to verify this, I found a few YouTube videos and checked the seat numbers in them. In this video for instance the seat numbers match up perfectly with the ones in your link.
TL;DR: The dropbox page you linked to from Seat61 is correct for the EuroCity-Express train as well as the Frecciargento.