Boo! was not a movie. It was a TV program name representing a movie with another title. I can't think of a better example right now. But Boo! was a name like Vincent Price Theatre or Tales From The Crypt or Mystery Science Theatre 3000. However, the actual movie is another title. Does that make sense? Thank you.
If you have trouble getting the first website, google 1970s tv program called Boo!
It will be the second link that you see.