So effectively before the anamorphic DVD is encoded the 2.35 image has black bars added to it to make it fill a 16:9 (1.77:1) screen.
If it wasn't an anamorphic DVD (i.e. letterbox) it would have much larger black bars added to the 2.35:1 picture to make it fill a 4:3 (1.33:1) screen.