I disagree with the currently accepted answer : furnishings includes pieces too small to be furniture, such as curtains, possibly wall hangings or paintings and so on.
A piano is a musical instrument and a pianist may be insulted to see it considered merely "furniture". However in some times and societies, it has also been a normal and expected part of the furniture in a civilized household, whether or not anyone plays it regularly - or slightly pretentious if nobody does. Or more than slightly pretentious if it's a grand piano.
So, listing a piano as furniture may be a sly way of telling us something about the household, and not necessarily complimentary unless one of the characters actually has some musical talent.
The "Chicago Tribune" quote in another answer turns this notion on its head, suggesting that its role as furniture is even more important than its music - and perhaps for their audience, that might be so.