I think that is true. Not having gone to any horror movies back in the day I can't tell you from personal experience.
I do have a vague recollection of a non-horror movie (I think it was a sci-fi) where having something external to the movie happening to the audience was part of the story - a movie (and a theatre) inside the movie. that may have been based on something.
Moving slightly off- topic, I think the best example of something like this has to be the
Rocky Horror Picture show. Which was not a horror movie but a musical satire of the classic 50s horror movie. It became a cult favorite and some theaters had a Friday night midnight showing all year long.
audience members would show up with props that would be employed at various cues during the movie. The audience also would shout lines back at the screen on cue. The musical numbers were almost sing-a-longs.
One time I was watching it and a dozen members of the audience climbed onto the stage in front of the screen and acted out the entire movie, in appropiate costuemes. In fact a lot of the audience sees the movie as an excuse for cosplay.
en.wikipedia.org