Democracy just means you elect your leaders and have more than one political party. Capitalism is a financial system, not a political one. That graffiti is like saying Firetrucks aren’t a vegetable (with the inference that they’re a fruit).

So Communism isn’t a Democracy, and Monarchy isn’t a Democracy, but you can definitely have a Corporate Capitalist Democracy.

Also, Capitalism itself has democratic traits, such as share holders getting to vote. However you do need money (capital) in order to obtain votes, so it’s not political system, it’s a financial one.