Review of the photos and schematic for the bed-base indicates that the merchandise concerned consists of solid oak wood, solid white oak wood and oak veneers over plywood, having four, black powder-coated metal feet. Photos indicate wood cross-slats, horizontally and vertically, within the frame of the bed-base, two additional wood support feet symmetrically positioned under the frame of the bed-base, and an underlying box-frame placed between each of the metal feet of the bed-base. The bed-base has no moving parts. The bed-base is assembled in two halves with wood dowels used for alignment and connecting of the two halves. Nothing in the photos and schematic suggest that the bed-base is or acts like a futon wooden frame, also known as a futon wooden base.
[1] Please importantly note that only the relevant portion of the related is displayed above. You may refer to the said customs ruling for the entire ruling explanation.
[1]. https://rulings.cbp.gov/ruling/N254191