As I understand it he says that Flutter uses dart and that is much better than js, react native lacks good documentation and the developer tools are great for Flutter/dart.
Both Flutter and Dart seems interesting but I don't think they will take over the world in 2018. TypeScript already exists and has a lot more users than dart and also has good tooling. It is also typed like dart which makes more traditional c# and java devs happy. React is getting more an more popular and react native will probably live on that, even if it isn't the best solution for building mobile apps (and it might be the best one yet, I don't know).
Both Flutter and Dart seems interesting but I don't think they will take over the world in 2018. TypeScript already exists and has a lot more users than dart and also has good tooling. It is also typed like dart which makes more traditional c# and java devs happy. React is getting more an more popular and react native will probably live on that, even if it isn't the best solution for building mobile apps (and it might be the best one yet, I don't know).