With no explanation, label text_A→text_B with either "DON'T KNOW", "NO" or "YES".
text_A: Young Fionn, still known by his boyhood name Demne, met the poet Finn Éces (Finnegas), near the river Boyne and studied under him. Finnegas had spent seven years trying to catch the salmon that lived in Fec's Pool () of the Boyne, for it was prophesied the poet would eat this salmon, and "nothing would remain unknown to him". Although this salmon is specifically called the "Salmon of Knowledge" in the text's narration, this fact is not known to the characters, and it is only presumed by them that it is the salmon that fed on the knowledge at Segais. Eventually the poet caught it, and told the boy to cook it for him. While he was cooking it, Demne burned his thumb, and instinctively put his thumb in his mouth. This imbued him with the salmon's wisdom, and when Éces saw that he had gained wisdom, he gave the youngster the whole salmon to eat, and gave Demne the new name, Fionn.
text_B: From the way that he behaves in the story, is it likely that Éces had heard the prophesy of the salmon giving the poet wisdom, and therefore knew that only young Finnegas could benefit from eating the fish?
YES.