If you’ve installed AnkiDroid from the Play Store previously, and you didn’t turn off auto-updating, it makes sense that it would update your app. You can turn off auto-updates to avoid that (as was suggested to the other user).
Or I think [not entirely sure this will work, but it seems likely] if you uninstall through the Play Store (at least), and possibly also remove the app from your “Library” – the Play Store should leave it alone, because it ignores side-loaded apps.
Make sure you have your collection synced/backed up somewhere safe before you start messing around with versions that are before/after storage migration.