You don’t need Windows for networking. There was lots of networking software for DOS. NetWare was the most popular, but there were heaps of alternatives: Microsoft/IBM LAN Manager, Banyan VINES, DEC Pathworks, Sun PC-NFS - most of those required a server running some other operating system (such as OS/2, Unix or OpenVMS), but there was also a category of “peer-to-peer” DOS networking software which could operate without a dedicated server, e.g. Artisoft LANtastic, Novell’s NetWare Lite and its successor Personal NetWare