A bit late, but for anyone experiencing the same, I would suggest to check the Installer of your app.
Using PackageManager.getInstallerPackageName()
getInstallerPackageName (String packageName) Retrieve the package name
of the application that installed a package. This identifies which
market the package came from
If the value is “com.android.vending” then the app was installed from the Play Store otherwise handle the other vendors.