How is The Truman Show a dystopian film?

A dystopian work imagines a nightmarish future in which the worst aspects of contemporary life are magnified. In The Truman Show, the aspects of contemporary life which are especially magnified are our fondness for reality television and the extent to which governments intrude into and monitor our lives. In the film, the government, in the form of the television company, is totally intrusive and monitors every moment of the main character's life, which is, in itself, directed purely for the entertainment of others as a reality television program.
Another aspect of dystopian fiction is the dehumanization of the characters. In The Truman Show, the main character is dehumanized in the sense that he is treated like an animal in a zoo—there for the amusement of other people. Truman's whole life is controlled so that he is reduced to a spectacle. He does not have any meaningful control over his life, and even his environment, like that of a zoo animal, is manufactured and artificial.