The old man was supposed to be practically blind by now. However:
the old man couldn't believe his eyes and almost cried to the signboard at the entry: TODAY SPECIAL: SEAGULL MEAT!
He can suddenly read, which means that during the stay on the island his eyesight was somehow cured. Apparently, seagul meat (or human flesh, when the other answers are also right) was the remedy for his condition.
He went outside and saw the palms on the island nearby. He had now fulfilled his live goal of seeing a palm tree and was able to die in peace.