I know I'm not a genius, but I've read the whole thing and I still have no idea how the bed was rearranged. Did I miss a diagram or something obvious like that?
It looks like the bed had spare wood (struts underneath or maybe a larger headboard), and he went ahead and cut (?) the sideboards in half, removed the excess wood from wherever, and added them in the middle of the cut sideboards (like a leaf in a table).
I imagine that if the mattress were removed, the modification would become more apparent. Alternatively, a "before" picture would also probably make it more obvious. But, who takes a "before" picture of their bed?