Part of the video measurement procedure is to take photos of your ear with a ruler on them for size reference.Working out the exact size versus proportions must need something to provide absolute size.
I wonder how accurate the final result is given the fact that you can tune it in azimuth and elevation manually since that shouldn’t be required with an accurate HRTF.
But what really puzzles me is the fact that they don’t simulate room acoustics, only the direct wave. In my experience this results in very limited externalization in the range of a few centimeters only.