The SDK (recommended for login) is set up by default to collect information and installs handlers for app lifecycle events as soon as the app is installed. The default is to do this without requesting user consent.
A rough summary of the data: (Ad ID, device, locale, phone network, maybe install referrer).
To attribute advert -> install, Facebook ads pass on an encrypted blob containing campaign information to the Play Store, this blob is readable by the app, and is transmitted back to Facebook where it's decrypted.
The setting: https://github.com/facebook/facebook-android-sdk/blob/fcd4ef...
Defaulted to true: https://github.com/facebook/facebook-android-sdk/blob/5fe6e2...
https://developers.facebook.com/docs/app-events/getting-star...
In any case, this is not how it's supposed to work in oauth, and it's definitely not required for it to work.
I suppose developers could pretty much use any generic oauth lib for the login purposes.
Seems to me, this is pretty much exactly how this works.