No, they created an architecture and decoupled their web framework from it.

Which was a poor decision, imho. Using React only makes sense with Flux, why separate them? Furthermore, the examples on React's docs use the pass-down-the-event-handlers madness, instead of using Flux. React+Flux is a good solution, but the documentation leaves a lot to be desired.

React components can be brought into any architecture. Using them with flux certainly simplifies many things, but by the same token, flux apps can be written using other libraries (react based like om, or even full frameworks like angular). The decoupling is good. It lets you try out a component from http://react.rocks/ without diving into a fully architectured SPA.