Yes, they are both a way of transporting data. The difference is that ethernet is a networking standard that uses a specific scheme of timer cycles and carrier detect sensing to send packets of data across a wire while not interrupting transmissions from other nodes on the network. The listed 2-meter minimum/100 meter maximum distances for copper-based ethernet node distances are a careful balance of distance needed for 1 timer cycle (1 meter), capabilities of the copper transport, and distance covered before timeout (100 meters). Not the best way to do high-bitrate point to point data transfers. SPDIF is a high-bitrate digital point to point connection. It doesn't have or need the overhead necessary to run on a network. With SPDIF you don't have frames, headers, carrier sensing, collisions detection, etc. Just the 1s and 0s.
