The flutter.dev page got rewritten to be more "marketing friendly" a few years back. docs.flutter.dev is still maintained by the engineers however.
Regarding who exactly contributes to Flutter, it's all on GitHub, so you can see the actual committers, e.g. https://github.com/flutter/flutter/graphs/contributors https://github.com/flutter/engine/graphs/contributors https://github.com/dart-lang/sdk/graphs/contributors
As for flutterfoundation.dev, it appears to be just Matt? Who used to be employed at Google and reported to me on the Flutter team but is no longer.
It's on the front page: "A Global Open Source Community. Supported by Google, open to everyone."
Compare https://go.dev/project which explicitly mentions that Google runs the show. The front page makes it clear that Google runs the language’s cloud infra. Plus there’s the Google logo in the footer.
The Flutter page never mentions who runs it. If it’s independent but sponsored by Google, there ought to still be people involved. If it’s owned by Google, it should be clear about it, and not just indirectly mention it.
Then this flutterfoundation.dev site... weirdly also doesn't say who's behind it. Presumably some outside folks? Maybe just the one person who wrote this blog post? But if it's called "Flutter Foundation" I would expect it to be more officially sanctioned?
Were I in the market for a UI framework, none of this would make me feel very confident.