It is, presumably, significantly smaller in dimensions than the island in the game though. As for their homeland being "destroyed by fire", I took this (and the name) to be in reference to the
ancient volcanic eruption on the island of Thera, which destroyed the island's population entirely. I suppose Cythera springs from around the same era, but instead of the population of Thera being killed, they are transported to another world, or dimension, or plane or what ever.
“Yesterday we obeyed kings and bent our necks before emperors. But today we kneel only to truth..."