Could it simply be that in the clockwise roll to the inverted position (having dragged the starboard wing as reported) the starboard prop made contact with hard the runway surface whereas the port prop only contacted the soft grass after inversion?
That picture helps a lot. The Starboard wing was missing from the flaps outboard, and there's very little evidence on the remains of a side contact of the nose on the ground, so the geometry of the triangle suggests that it's unlikely that the blades made ground contact with the runway, although it's possible that they did so after the roll to inverted was complete. There's no overhead shots of the debris trail in the public domain to give a clearer indication of what started happening when yet.