Center hub pivots on a short spindle inside the hub. Much like an I-beam axle only centered relative to the tire with a zero scrub radius. Caster remains the angle of the pivot with the vertical. If mounted in a single swingarm, caster angle changes as the suspension moves.
The focus-link arrangement is using two 4-bar linkage systems. One set controling pivoting in the vertical and one set for the horizontal. A four bar can approximate a pivot but on this, trail moves a bit with suspension travel and trail and camber have a unique pattern of movement with steering angle.
Thanks Blue.
I'm still trying to convince Solidworks to generate the ports in a head I want to test, so a long way from having motive power. If I get the power, you'll see a two wheeled streamliner with focus-link designed.
It's fun here, learn things.