"Server" is a term of art. In this context, it refers to the fact that your home server delivers files and data to client applications that make requests for appropriate data, i.e. data the server
knows how to deliver, in an appropriate manner, so if the server requires authentication before it will deliver the data requested the request must provide authentication.
Put another way, "storage appliance" is more correctly considered a subset of "server".
So in the end, yes, your home server is a "server".
I'm not on the WHS team, I just post a lot. :)