artifacts – multi-strobe-like motion blur outdoors?

This photo (cropped here) appears on p. 48 of the October 2020 issue of the Experimental Aircraft Association’s Sport Aviation magazine. The upper blade of the propeller shows the motion blur that is typical of airplane photographs, and that is found in every other photo in the magazine article.

But the lower blade of the propeller appears as a dozen closely spaced distinct blades.
What could explain this? The photographer, Jim Busha, assures me that he used no strobes, nor did he use some exotic shutter technique or other arcane settings on his camera. The color looks like evening sunlight, contrasted to the cyan daylight illuminating the other blade and the fuselage. (Other photos show that both the prop and fuselage are mostly black and near-white, with olive-green mountains.)

crop of photo of airplane