In The Odyssey, how do the suitors become aware that Telemachus has left Ithaca and may be accompanied by a god? Book 4
Traditionally, the gods have stood by Odysseus, so they may continue to provide the same service for his son Telemachus.
Neomon actually lent a ship to Telemachus. Readers learn this in these words he utters to the suitors who had agreed to not let Telemachus go anywhere:
As for those who went with him they were the best young men we have, and I saw Mentor go on board as captain—or some god who was exactly like him. I cannot understand it, for I saw Mentor here myself yesterday morning, and yet he was then setting out for Pylos.
Thus, the god they assume to be with Telemachus is Mentor. Although Telemachus had been gone on his voyage for days, they had assumed he was up in the hills on a farm. Reality told a different story. This led them to fear what Telemachus was achieving and they gathered a ship themselves and vowed to go and find Telemachus.