Looking at the little bronze bush in the middle, I think it's possibly a sort of "ball joint" that allows the four-way movement of the button. Out of interest, if you apply *very* gentle force to the four little "buttons" or contacts in the cut-outs in the "cross", do they actually depress at all? If they don't, my guess is that the button is made of a conductive plastic that bridges the circuit between each of those little contacts and the central bush.
It looks also as if there is some sort of bond or adhesive securing the cross to the body.
John Gruffydd Mold, Wales, UK D300, D200, OM1, OM2n, Bronica ETRSi, Lumix LX5