I googled the names of the people holding the talk and they're both employed by Microsoft as software engineers, I don't see any reason to doubt what they're presenting. Not the whole start menu is React Native, but parts are.

It is funny how quickly this became normalized. During Vista time everyone was absolutely shitting on awful performance, now that PCs became faster it is apparently fine to use one dog ass slow managed language (C#) over another (JS with RN).

Even though RN for Windows is just a thin wrapper over WinRT, but who gives a shit, right? Because JSLOLLOLOL.