For the Play Store it doesn’t matter how an app is produced, it is a package that changed.
Probably Play Store is also not differentiating in showing the download vs. the update size but downloading a smaller file in the background.
I have check, it is a full download.
I purposely download a data manager to check when I update the app. It is 10 MB download for update the app.
Do you mean package version change. Example. 1.0.0 to 1.0.1 in config.xml, there shall be a differential update. If config.xml does not change to 1.0.1, then it will be a full download for the updates?