The film occurs as a form of social activity refers to the film as a dynamic media. There is a change in the context of social change, as well as media from the truth of different societies.
The film happens to be a form of social media, referring to the film's non-stop. Changing the social context. That changed as well The media is caused by the fact that society's different.
The film caused a social activity, form one means the film medium is not stopped. Changes to the context of social change as well. As the media of the truth of the society is different.