alt Hacker NewsThere are famously capitalist countries that are monarchies (like the UK), so as written that has to be wrong. There isn't really a definition of what "capitalism" means, although we can be fairly confident it involves people owning capital. Arguably it means that the people who own the capital should control the lion's share of political power (which, coincidentally, is how the US works).
The thing that makes communism (and fascism to a lesser extent) anti-capitalist are that it rejects the idea people should be allowed to own and control capital. So there is a clear incompatibility with communism even if the exact nature of capitalism isn't clear.
> Arguably it means that the people who own the capital should control the lion's share of political power
The ideology, such as it is, doesn't have to explicitly say that capital should have political power. It merely says that it's a moral outrage to prevent the rich from spending their money however they choose.
But the ideology is secondary to capital anyway. If we let the rich get rich enough, that's strong incentive for inventing ideological justifications for it; after all to be friends with the powerful gives an easy life, and to be their enemy give a hard one.