I would guess style and materials. Glad to see that we can put that mid 20th century dating to rest. The only thing mid 20th about these is the (re) upholstry, which looks more like 1960s or 70s.
I would think the chairs are closer to 1880 than 1860, but there you go.
And while we're at it, thanks mucho for actually going to the trouble to come back to update us!! So many just pose a question, then you never hear from them again.