does that really matter in terms of HOW the prop blade is moving the air? Isn't the fact the air is moving in a particular manner the important issue? Not what is making it move in that manner.
I think we are attempting to point out that the patterns in the oil (or dirt trails) do not show how the air is moving.
Think about watching rain streaks on your car windows. If you travel slow enough, gravity moves the rain drops straight down the window. As you pick up speed they get angled back, but you wouldn't assume the air flow is angled in the direction of the streaks until you are going reasonably fast.
Now consider that the oil on the propeller blade is subject to > ~4,000 G's outwards from the prop hub (rather than 1G for the water on your window). Also assume that the air flow (what we actually care about) over the propeller is more-or-less aligned with the chord of the propeller and interacts with the oil film through skin friction drag.
Any reasonable set of numbers I try has the centrifugal forces dominating by such an extreme amount (30-100x) that to draw any conclusion that the airflow doesn't travel approximately in the direction predicted by over a century of propeller theory would be premature from the presented evidence.
Here's the equation I derived for anyone who cares to criticize my math. It's probably impossible to calculate an exact answer, but showing that there's really no contest between the two forces is not difficult.
Centrifugal force magnitude at propeller tip relative to aerodynamic force =
4*(oil film thickness)*(density of oil)/((skin friction drag coefficient)*(density of air)*(diameter of propeller))
I estimated .0041 for the skin friction drag coefficient. There's a lot of small numbers in the denominator and only one small number in the numerator (oil film thickness).