I just re-read it again. You need to!
You’re confusing business corporation with municipal corporation. They are not the same thing! Generically a corporation is any group authorized to legally act as a single entity. There are many kinds of corporations. A municipal corporation is a corporation to organized a district inside a state inside the United States. Most U.S. cities and counties are municipal corporations of some form or the other. My hometown went from unincorporated - no city government therefore no legal way of acting as a unit to incorporated - a corporation now capable of acting as a unit having a police force, taxing power, etc. in 1948. The act (Again read the act!) dissolved the charters of Georgetown & Washington City and absorbed them into and under one municipal government called the District of Colombia which out of habit just say Washington. Read the act!
Funny how all the “fact check” sites insist “the Organic Act of 1871 did not make the United States a corporation.”