The person performing that task is not "acting like" a control system, they actually are controlling the prescribed variable. The hypothesis is that living organisms are, in fact, constituted in this manner, with many control systems in a particular hierarchical arrangement. That every action they perform is an output action of a control system that is endeavouring to keep some perception at some reference level.

Indeed. I don't disagree with anything here.

What I'm trying to say is that the ability to control one variable doesn't provide much evidence for "it's control systems all the way down". One might as well claim "The brain is a finite state machine" because we can simulate them using pencil and paper.