In an emergency situation, when one has to remember to do A, B, C, D, etc, some steps can be forgotten, or done out of sequence by a pilot not intimately familiar with the plane.
My guess is Bong wasn't intimately familiar with the P-80 and when the fuel pump went out, he either mid-diagnosed the problem, was too slow reacting, or forgot what to do.
From Yeager's book, Yeager. Bong reportedly had the ego sickness which many managers and fighter pilots have: Ego Sickness. Reportedly, after being pulled from combat, he was testing out the new P-80 fighter plane, and the factory technicians tried to explain the characteristics of the aircraft. He would not let them because he was Dick Bong, the Ace of Aces and didn't need to receive instruction from nerds... Crashed on takeoff. Killed.