You think Lumak is trying to tell you that he can no longer help you improve your fishing skill. You may want to try to find his friend, Nat Pagle, a human fishing off one of the islands south of Theramore (at least that's what you think Lumak said).
Lumak no can teach [player] no more. You too good! Find Lumak friend, Nat Pagle. Is human but no eat! Is Lumak friend! Nat teach you fish gooder.
You find Nat in Dustwallow Marsh, south of Humie town, Thermorosomethinglikedat. Nat probably fishing. Go now!