It means that they aren't on their home world, they are "wandering" lol.

Basically my Home World is Siren, and my FC tag says Rebel. But if I world visit to Gilgamesh my FC tag is removed and replaced with Wanderer to show that I'm not "native" to that world.

Your home world appears to be Atomos, so if you were to visit any other world on your data center you'd get the Wanderer tag too.