woulda been weird to call it "Washington" when they named it DC because Washington was standing right there. Also I advise not looking too deeply into who this "Columbia" person is because whooooo that gets weird in a hurry
I hear it referred to as DC a lot. The other one that's funny is the metro area is called the DMV (DC, Maryland, Virginia) which is also what we call the department of motor vehicles.
Fair, since any state gets referred to a lot, but also SF and DC are major cities that get referred to more than some states.
Most folks I know just call it DC, but I live here 🤷
Also sometimes (pretty rare) DC IDs get rejected at bars because "DC isn't a state" so our IDs say Washington, D.C. now