If I had been that child, I would have panicked, too.

Think about it.

Here you are, with probably a sensory system that really over-reacts to touch. There's a flight attendant coming up to you and randomly yanking on your seat belt. It's painful. It feels like a shock to you. You quickly loosen it. She comes by and yanks on your belt again. This time she yells at you. The loudness and hostility of her voice starts to make you desperate. You can't figure out what you did wrong. You start crying. She yells at you again. Your ability to figure out what she's saying starts to go down the tubes because you're so stressed out. Your mom's trying to make you sit down. Finally you just can't take it anymore so you rip the seat belt off and you just fall to the floor and start crying in earnest...

People should know not to go yanking on people's seat belts and yelling at them if they are autistic and already in a stressful new situation like an airplane flight. The arlines need to educate their flight attendants.