When I was little I thought fire was the secret ingredient to make things go fast. How did rockets reach outer space? They had fire coming out the back of them. How did race cars get a super-speed boost? Flames came shooting out the back. Even jet packs had flames shooting out of them.
So it wasn't totally unreasonable that I thought the same thing applied to paper airplanes. When I was little I made a paper airplane, went outside with a match, lit it on fire, and was totally expecting it to fly off for a few hundred feet. Instead it nosedived after about 0.01 feet and slightly smoldered on the ground.