Sorry about the late reply.

I don't have access to an apk of paid Boost for Lemmy, but this is what Exodus Privacy has to say about it: https://reports.exodus-privacy.eu.org/en/reports/com.rubenmayayo.lemmy/latest/
The app does not have Lemmy in the name, but I assume it is the Lemmy version because of its package name

You can also check it locally by
a) installing App Manager from F-droid, and when they boost app's details are opened, use the Scanner feature. It is a larger action button in the vertically scrollable button bar below the app name
b) export the APK to your computer, and use JADX from github to disassemble the APK. you should be able to see the layered packages and source code of the embedded trackers.

Yes, what you described is app flavors, and is a feature of the android sdk. However, the dev probably didn't remove the dependency incisions. Even if they now don't issue a specific initialization call at app startup, the tracking frameworks have registered their own content providers and broadcast receivers in the androidmanifest file at build time, which will be started at app startup before other components of the app.