In Hatchet, what did Brian do that attracted the fish?

Gary Paulsen's 1987 novel Hatchet tells the story of a thirteen-year-old-boy, Brian Robeson, and his journey to survive in the wild. While on a small passenger plane with only himself and the pilot, Brian is thrown into a life and death battle after the pilot suffers a heart attack and the plane crashes. The only survivor, Brian is stranded in the deep wilderness of northern Canada and must learn to use his hatchet, a gift from his mother, to survive on his own in the wild.
Brian's plane crashed near a lake, and he quickly becomes determined to figure out how to catch some fish. He tries several methods. First, he wades into the water and stands very still and then tries to catch a fish by hand. When that is unsuccessful, he decides that he needs to create a wooden spear with two prongs at its end to capture the fish. However, this method also does not work.
Finally, Brian realizes that he can finally become faster than the fish if he creates a bow and arrow specifically for catching fish. Using his hatchet, he creates a small wooden bow and then crafts wooden arrows out of willow branches, shaping their ends into points and prongs. When Brian tests his new invention, he is at first unsuccessful. However, he suddenly realizes his mistake.

Of course—he had forgotten that water refracts, bends light. He had learned that somewhere, in some class, maybe it was biology—he couldn’t remember. But it did bend light and that meant the fish were not where they appeared to be. They were lower, just below, which meant he had to aim just under them. He would not forget his first hit. Not ever. A round-shaped fish, with golden sides, sides as gold as the sun, stopped in front of the arrow and he aimed just beneath it, at the bottom edge of the fish, and released the arrow and there was a bright flurry, a splash of gold in the water. He grabbed the arrow and raised it up and the fish was on the end, wiggling against the blue sky. He held the fish against the sky until it stopped wiggling, held it and looked to the sky and felt his throat tighten, swell, and fill with pride at what he had done. He had done food. With his bow, with an arrow fashioned by his own hands he had done food, had found a way to live.

Later, Brian learns that he can section of part of the river to create pond for luring fish into with bait. The fish swim into the pond and into a fine mesh net that Brian has created by weaving fine willow branches together.

Storing live fish to eat later had been a major breakthrough, he thought. It wasn’t just keeping from starving—it was trying to save ahead, think ahead. Of course he didn’t know then how sick he would get of fish.