Is it possible that the coil is ringing in the unloaded (last) photo, and that the small light globe acts as a snubber?
The harmonics seem very linear in their"fading away" from the  principal freq.

It is not what I expected, but upon thinking about it, I guess this is the price of having the teeth letting go as they pass the magnet, and experiencing a "twang/shock" in the magnetic field as the flux lets go of one tooth and realigns onto the next. This would have to show up in the impedance of the coils.

Even thinking about it, I would not expect to see this in the axial flux design.