It’s just means the signal is there, since SPDIF_TX is on gpio pin 7, so you do have 1x SPDIF output. The word “optional” is kind of important there too. 
Adding the Toslink connector is as simple to do as adding an led is.(which it pretty much is) Adding an RCA connector requires some more know how and a few more parts, since directly trying to drive a 75ohm cable from the soc pin is a really bad idea.