It was mentioned by Tony Baxter as what was explained to him for the reasoning of the descent, and it was part of the story in one of the 1969 promotional records that narrated a ‘ride-through’ and described every scene as if it were a story.
It also ties in to the ‘falling to our death’ idea. The Claude Coats half of the attraction has darker tones and the spirits do not seem friendly. The attic is the epitome of this, as (especially in the 1969 version) there is nowhere in the rest of the attraction where the ghosts seem most malicious than in the attic. As the story goes, you’re scared out onto the balcony and fall to your ‘death.’ After this point and into the Marc Davis half of the attraction, all of the ghosts are friendly and seem to want to party with you, almost like you’re one of them now. This idea wasn’t mentioned in any promotional records like the other, but it’s been stated by a few imagineers and makes sense from the rider perspective!