The passage you quote comes only two pages after Ged's first encounter with terrifying magic:
As he read it, puzzling out the runes and symbols one by one, a horror came over him. His eyes were fixed, and he could not lift them till he had finished reading all the spell.
Then raising his head he saw it was dark in the house. He had been reading without any light, in the darkness. He could not now make out the runes when
he looked down at the book. Yet the horror grew in him, seeming to hold him bound in his chair. He was cold. Looking over his shoulder he saw that something was crouching beside the closed door, a shapeless clot of shadow darker than the darkness. It seemed to reach out towards him, and to whisper, and to call to him in a whisper: but he could not understand the words.
The door was flung wide. A man entered with a white light flaming about him, a great bright figure who spoke aloud, fiercely and suddenly. The darkness and the whispering ceased and were dispelled.
Impatient with the slow pace of his education under Ogion, and eager to impress the girl he's been spending time with, Ged tries to perform magic that he's not ready for yet. The result is that he apparently summons some form of evil into the house, which only his master is able to dismiss. Note the use of the word shadow to describe the thing that appears and whispers to him.
Ogion then warns Ged about the danger inherent in the practice of magic:
“Ged, listen to me now. Have you never thought how danger must surround power as shadow does light? This sorcery is not a game we play for pleasure or for praise. Think of this; that every word, every act of our Art is said and is done either for good, or for evil. Before you speak or do you must know the price that is to pay!”
Again the word shadow is used as a metaphor for supernatural danger.
A mere two pages later, when Ogion is enquiring about a ship to take Ged to Roke, they are told about the ship called Shadow. Doesn't it seem like an ill omen?
(Of course, all of this foreshadows [pun unintended] later events in the story, the appearance of a much greater and deadlier "shadow" to a more experienced and knowledgeable Ged, which then dominates much of the narrative thereafter. But even now we've already seen enough to appreciate that the word Shadow carries dark connotations.)