Here's why:
* Polyphemus's Legacy: In the original Greek myth, Polyphemus was the son of Poseidon. After Odysseus blinded him, Polyphemus vowed revenge. He fathered many children, who inherited his cyclopean traits (one eye and large size).
* Island as Home: These descendants of Polyphemus settled on an island, which became their home and territory. This island is likely the same one in *The Sea of Monsters*, as it's known for its cyclopes and its location near the Sea of Monsters.
* Not All Evil: While Polyphemus was hostile to Odysseus, his descendants are not necessarily inherently evil. They are simply a different species, with their own culture and traditions. In the book, some of the cyclopes are friendly to the heroes, while others are hostile.
So, it's not about "other cyclopes" on the island, but rather the descendants of the original cyclops Polyphemus, continuing his legacy in their own way.