I don’t think that’s what he is talking about here though. And note, his point about the multiple files isnt even a complaint.

As someone who worked with Ember in the past (our company inherited a new product with an acquisition so we were forced to change tech stacks), this comment really comes from the fact that Ember has a very comprehensive file layout system. And one of the major criticisms about Ember classic was how different core pieces for the same component, were located in so many distant folders (hence the comment about colocation of component code, which seems trivial, but is a huge usability gain IMO).

I think that sentence should be read more as a reflection on Ember, than suggesting the author does not think React components can be broken into multiple files, and hence an indication of their knowledge of react.