First of all, with my automatic this would not work for me. Even in my 5-speed 4Runner, I would not do that. E-brake is the most effective technique IMO, and it's what saved us. Here's why, I think.
I used to race dirt track modifieds. They don't use much front brake because if your front locks up, you can't steer. On the other hand, you poke the rear brakes, weight transfers forward, and you can steer. Same thing here where it is so slippery, especially going downhill. Slightly setting the E-brake loads the rear brakes so even when you start poking or pumping the brakes, the weight transfers forward without locking the fronts.
Some people say hit this gas when you are sliding downhill. That transfers weight to the back and although you could steer again because the fronts aren't locked, you have to be able to stop the momentum you are gaining soon or the problem is worse. That would have been bad for this Spooky Night Run because nobody knew when they could stop. Probably a good technique for more of a Red Cone situation where all that matters is not sliding off the side.
Going into reverse while moving mimics the correct weight transfer but it's harsh, and out of control. Reverse is for rotating the tires in reverse, you don't want that you just want to use the rear tires to transfer weight to the front without locking the front so you can steer. E-brake does this precisely, predictably and in control. You could even lock the rears and drift down the hills and still be in control because you can steer and modulate the rear handbrake. Maintaining control is priority.
This is my hypothesis, I have no proof, just my opinion. And like the football commercial, it's only weird if it doesn't work. Everybody got the job done that night. In situations like that you can't hesitate and you must trust your instincts, if reverse saved you, I believe you made the right call.