No, this is just a simple story to help illustrate the concept
of a negative control.
If we give a medicine to somebody, and he feels better, that
doesn't mean that the medicine necessarily worked.
In clinical trials, patients are separated into treatment and
control groups. Control groups only get inert pills.
If both groups got equally better, then the medicine is not
effective.
If the treatment group got much better, than the medicine is more
trustworthy.
In order to know whether an invisible magic stone itself can
produce soup, you must remove the other ingredients.
If the other ingredients cannot be removed, you cannot ignore their
contribution to the soup.
In fact, if the soup is the same without the invisible magic stone,
then you don't have to factor in the effect of the magic stone at
all.
