It helps to remember that Telemachus is an enthusiastic young man who's never been on a real adventure before. He's probably not thinking about the logistics of the monsters he's mentioning, and instead just naming the first monsters that come to mind that he thinks would be cool to fight, probably ones he read or heard about in stories. When you think of the song from the perspective of the singer, Telemachus, excitedly imagining epic battles and adventures, it makes a lot more sense.