Interesting. I did a semester in school with pinhole, and the proffesor gave me comments wondering how I got mine to have excellent contrast where typically the pinholes are washed out. I didn't have a good reason and was unable to answer the question.
But now. My pinhole was recessed into a large format shutter to the point that the threads for the lens elements where visable in the frame. I bet this was acting as a lens hood giving the images and added punch.