It is possible to work directly with C++ though, which I think Netflix must be doing with their Gibbon framework because their interface is very different from

It is possible to work directly with C++ though, which I think Netflix must be doing with their Gibbon framework because their interface is very different from those obviously using the Roku tools (and looks exactly like their interface everywhere else). As the article states, Netflix aren't necessarily working with HTML when they make these React views - it sounds very much like how React Native works.