It is of my opinion that the wire is on top of the plate, that is between and the screw head where the screw should actually be lostened to a point where the wire can be inserted under the plate and wire alligned with the channel on the bottom side of the plate. The screw is tightened down securing the plate against the wire.I have seen brass plates that look like this but they do move. Guess we need actual part number to know for sure. Your closeup shows the brass is not a 'flat' plate, it definitley has a groove in it under the screw. This is for trapping some type of wire.
I would also confirm that the device is listed for terminating the wire that is being used.