I think I can see what they are getting at with this expression here.
There is a style of furniture that, even though it does have comfy cushions, has a largely exposed wooden frame — at one time, this kind of furniture used to be referred to as "cottage-style"; this is as distinct from what they are referring to here, which is, I believe "fully-upholstered" — i.e. the whole thing is covered in fabric, so even though these people are carpenters, their workmanship won't actually be visible!
Sadly, this term has rather changed its meaning over the years, so a modern image search returns precious few relevant images; but here is just one I found that shows the style of furniture I think they are contrasting with:
https://a0.amlimg.com/NDU0NWNmOTc2NTQ2NThjNGJkOGQ4NWRiZGE0ZT...While this is a more classic rendering of what I would consider an "upholstered sofa":
http://img.archiexpo.com/images_ae/photo-g/57305-4324047.jpg