They didn't start getting large numbers of reports like this
until AFTER "Close Encounters of the Third Kind" was released.
Similarly, until the series of Flying Saucer movies in the early 1950s, reports of saucer-shaped vehicles were almost nil. Even the famed report from which the term "Flying Saucer" was coined, the object were not described as saucer-shaped, but rather as "skipping like saucers over the water."
Life imitates art. Fantasy-prone persons can not differentiate between memories of movies and things that they saw in the sky.