Hmm...wouldn't it just be forced to stay on the ground whilst falling? I mean, the example portrays a balloon contained within a car with no air resistance falling off the cliff, and the moment the car falls off, the string cut off. My assumption would be that the force of the car, when freefalling, would force the balloon to stick to the floor. I'm probably wrong with this assumption of mine, and I have another one in mind, but I also believe I'm wrong with that one. Also, I don't know if sea level/elevation plays a factor in this experiment.
The air pressure inside the car would be greater than inside the balloon, so the balloon would be forced to the bottom of the car... Don't know, would need to think about it more thoroughly.
Took me 10 minutes to think and email the answer and I'm still not sure if I'm right. I just want that t-shirt.