The correct statement is: "His kinetic energy increased while his speed increases, then it became constant."
As the skydiver accelerates and increases his speed, his kinetic energy also increases, since kinetic energy is calculated as \( KE = \frac{1}{2}mv^2 \), where \( m \) is mass and \( v \) is velocity. When the skydiver reaches a constant speed (in this case, 50 m/s), his kinetic energy remains constant as long as his mass does not change.