I don't doubt that their test resulted in minor penetration. I'm just saying that stuff happens.
I mean, come on now...a cloth bag full of lead shot hitting just right so that it cuts instead of deforms? It almost never happens, but it has happened a few times and it killed someone at least once. And by kill, I mean that it penetrated and killed; had it deformed as designed, it would not have killed in this particular case. (It's worth mentioning that this particular phenomenon also involved the beanbag "inflating" and travelling like a disc at unexpected times, causing it to deviate from its point of aim; this may indeed have contributed to at least some of the injuries.)
Keeping all of this in mind, if the optimal shape for the projectiles in a shotshell were thin discs, we would not be fooling around with this shot business that we're currently using and we'd be referring to shotgun ammunition as "discshells" or something similar. (And please no one bring up quadrangle, as that's something entirely different.)
Einstein didn't like quantum physics because it didn't make sense to him. Quantum physicists avoid exterior ballistics because it gives them headaches.