you cannot tell someone is autistic by simply watching this clip. everybody gets scared by loud noises specially when you don't expect it. and the reaction of the laughing lady is normal, don't be too serious dissecting people's reaction. have a life!
This child may have autism and so be sensitive to loud noises as completely over stimulating and painful. The waiting close up of the camera and the knowing laugh of the nearby lady, presumably in the family (why would a stranger laugh at someone else’s crying child?), indicate they knew this response would come. An autistic child's behavior would be characterized by fear responses to such loud stimuli. This borders on torture (although ignorant I hope) of a mentally challenged person.