As far as the bit about Flutter goes: Flutter was started by engineers from the Chrome team, and myself (who worked in the open source team as editor of the HTML standard). We had no relationship with the Dart team at all until some times into the project, when we were looking around for a language to replace JavaScript in our project (codenamed Sky at the time). We considered a large number of languages but ended up picking Dart because it was the best fit (see the Flutter FAQ for more details). We then had to learn Dart and made friends with the Dart team, with whom we now work very closely.
I wish I had our notes from back then, but I looked for them recently and couldn't find them. Our best theory is we did it on paper or on a whiteboard. :-(
I thought that flutter was started outside of Google.
Here is what is happening :
A couple of years ago, when the dart team failed at getting their runtime embedded into the browsers, they started searching for a problem to solve. They thought they had hit jackpot with multiplatform development. So they started working on Flutter. This is all entirely independent from the Android team at Google.
The Android Team at Google continuously improves their own framework, hence the jetpack set of libraries. One of the new libraries they have been working on and that is now public in pre-alpha stage is JetPack Compose. They have hired one of the engineers behind React and had them work inside of the Android Team on a "React like UI framework for Android".
The official direction of the platform is what the Android Team is doing.
Flutter is interesting, with all the advantages and caveats shared with other multiplatform tools like ReactNative.