I could find git repository/branch for Brillio but no separate for Android things. Is it that it is not open source yet or released for public ?
No because AndroidThings is still in preview as you can see from this link:
https://developer.android.com/things/preview/releases.html
the source code is not available.
There is a GitHub page though with the examples of how things are built on Android Things:
https://github.com/androidthings
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