Also, while all Dart does for Angular is fragment the community (because now we have Angular web devs using Dart, Angular web devs using JS and soon Angular web devs using AtScript), React Native actually does the opposite.
A lot of web devs already also do mobile development or at least work on hybrid apps (i.e. WebView-based mobile apps). React Native enables web devs to develop mobile apps that wouldn't have been feasible before (either because of the limitations of WebView or because they would have had to worry about learning an entirely different stack that is orthogonal to their web technology knowledge).
Wait, can you quote where they said that. Maybe a particular time in the video...
angular_devs ∩ dart_devs ~= 0 (relative to angular_devs) react_devs ∩ mobile_devs ~= react_devs
Almost everyone who uses react also has to do mobile development, and would like a simpler way to do it. This solves a real and widespread need.