This is what writing is: you throw a lot of stupid stuff at a wall, then see what sticks. And you never really understand it enough to do it like that again, and, meanwhile, people say it means this and that, and for reasons you can’t figure out, the story lasts, even though it was just something you thought might make someone smile:
http://www.vulture.com/2017/10/david-s-pumpkins-oral-history.html
As for where I think the humor in this is? The effort to intellectualize a non-sequitur, instead of just feel it—as the couple is forced to do at the end. Which, yes, would be me attempting to intellectualize the basically unintellectualizable . . .
In short? Horror isn’t about thinking, it’s about feeling. Which, no, wasn’t remotely the intent behind this sketch. Too, though, the thing with art, it’s that you can get from it whatever you need, regardless of what the artist meant.