The AC would cause a shifting of north/south poles...
Yes, a linearly oscillating field could be generated in the bore with multiple bucking windings ...maybe a rotating field.
A rotating field generated with 2 terminals only ? How ? A thick shorted coil could create a phase-delayed shaded pole but I do not see one. Anyway, normally, rotating magnetic fields need a squirrel cage type rotor to grab onto. How this would cause a steel shaft to turn I don't know yet,...
A solid steel shaft can be spun by a rotating magnetic field using the shaft's ferromagnetic hysteresis but the effect is very weak. Especially at low frequencies. A solid steel shaft can also be spun by a rotating magnetic field using the eddy-currents induced in the shaft, but without the squirrel cage, for this effect to generate enough torque to overcome even the friction of the bearings, the AC frequency has to be very high and the inductance of the windings must be low because i=V/X L. The windings visible on that toroidal core are of the high-inductance type. They are incapable of supporting large high-frequency currents without insanely high alternating voltages. ...its very interesting and strange.
It seems like you have identified a mystery.
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