Oh yeah you're absolutely right of course. Not saying it doesn't run V8 or some kind of interpreter in the background (I actually have no idea how they work), just think that's abstracted away and I don't think there's any JavaScript setting up required from the developer.
React is implemented in JS and uses JS to declare components, and it would be fun if there is some working JS-to-Python (-to-PHP/-to-Ruby) translator that is good enough to translate React code to run "natively".