I believe this could have been inspired by a story I read way back in the 1960s about a family that waylaid solo travelers who were unfortunate enough to stop at their out-of-the-way home diner in the woods.  The victim was seated at a picnic bench set against a canvas room divider.  While the diner enjoyed the victuals, one of the family members would step up behind the guest on the other side of the tarp and whack them with a sledgehammer.  Eventually, the victim returned to the table, but this time as the meal.

Since I no longer have that particular book I've got no way of knowing if this is a true story or merely an urban legend, perhaps influenced by the Sawney Beane saga.