It might, but I think it's equally possible he's right. For example, had Angular 2 not come out the way it did... it probably WOULD be in the mature column (I personally have found myself extremely productive in it), but adoption was hindered after people found out about the breaking changes in 2.0 (I personally hesitated for the last 2 years to start a new project in it). React is close to mature, but I kind of get the feeling it's accelerating not because of it's own merits, but rather it filled a vacuum. Adoption not earned by being "the best", but rather "the product everyone is talking about" does not bode well in the long term. Don't get me wrong, I think React has a lot of positive qualities, but I think a good framework should make a problem no more complex than the problem itself is. If you start using flux frameworks etc (as is expected with React) I really start to feel like I'm wasting time on things that are not the problem I'm trying to solve.
I wouldn't call Ember "challenged" though, since it's evolving constantly and adding features inspired by a lot of new tools.