You say it better than I do. Agreed it's an extreme selection bias, just want to point out that it's slightly different than the one de Boer seemed to be pointing out.
It's still the same bias he argues, the three percent are the most motivated and prepared. Why the other 97% skip it isn't relevant in this argument, but the number is independently shocking without the context. I fell for it until the ND mention, and I took the ACT.