I think the point, which I agree with, was that in the typical case of a stock rejection, you don't know if the errors you think you made had any bearing on the decision. Information you get from the process you would have gotten whether or not you got accepted, so it's not from the rejection.

There are cases where the company gives you some indication of why they rejected you but they are rare in my experience (in the USA, mostly for legal reasons, IDK about other countries). Or they give you information in some other way. Some companies will stop and send you home part way through if it's not going well. That also gives more information.