Cyclops are visibly larger than travelers, about the size of an ogre, plus Cyclops have one eye and travelers are normal humans with two eyes.

Surely it is a detail that you missed and it is unfortunate that the SMS team has left letters with Lore scattered throughout the game so that in the end no one has noticed it.

Anyway, both in The Lost Pages of Norse Myth, as in the God of War Lore and Legends book, and in the Lore's writings of the game, it is said that the travelers are warriors recruited by Odin to find the secret way to Jötunheim. We find many bodies of travelers killed during the game and a quest of wayward spirits in the Lake of Nine tells the story of an Ex-Traveler whose crew was sunk by Thor as revenge for betraying Odin. Or at least that's what he believes. Later in the lake you find a letter from one of the crew of the spirit that tells that he and a few men stole treasures from a temple against the captain's instructions, so during the storm that sank his ships, Thor appeared in a kind of vision and told him that this was the payment for robbing the gods.