Turn most chairs around and you find out what they really are.
The outside back is where cost is usually taken out of a chair. It is the surface nobody photographs, so it gets a plain panel, a cheaper cloth, or a stapled skin with the tacks showing - on the reasonable assumption that the chair will spend its life pushed against a wall.
That assumption limits the chair permanently. A piece with an unfinished back can never float in a room, never sit at an angle across a corner, and never stand at the head of a table where people walk behind it.
So this one is close-covered on the outside back in the same fabric family as the inside, pulled and finished properly with the edges trimmed rather than tacked. The upholsterer does the outside back last, working from the top down, so the final line of trim closes at the bottom rail where it is out of sight - the only place on the chair where anything is hidden at all.
It takes an extra day and a meaningful amount of material. What it buys is a chair you can put anywhere in the room rather than only against its edges.