I suppose in a very general sense a HomeGroup/Workgroup could be loosely defined as a peer network, but only in so far as there is not a server (As in Microsoft Active Directory Domain Controller) in place overseeing network resources and security and all network nodes are basically equal. But truly it is still more like a client server environment in that each node determines what they are sharing and who has access to those resources.
A true peer to peer network is really more like some of the common file sharing programs like (Napster, ShareBear, Morpheus, LimeWire, uTorrent, etc.,) where the program establishes the sharing, and exposes those shares as "Seeds" to other computers running the same program, and makes them generally...