Rear triangle pivots around an axle behind the BB. Observe that it swings freely, i.e. it is not fastened at the peak to the seat tube, but merely aligns to it where the grey, slightly- conical, rubber element meets the frame (an ordinary doorstop by the looks of it, doubling as the bike's suspension, of sorts). The rider's own weight provides the necessary stabilizing mass, and the gravity does the rest.
    Note the integrated bicycle pump, small French "afa", capable of producing the recommended tire pressure of 75 PSI. The two black conical objects above are one pair of a quartet of castor wheels for wheeling it around. And, to top it off, the rear carrier of the T models contains even two integral bungee cords with plastic hooks to provide a minimum of an ever- present tying- down capability for transported items.