iOS app retains data between installs? I recently installed VLC on iOS 10 and noticed that there is play history in it on a fresh install. 

How does this app preserve data between installs? Should it even be able to?

It doesn't matter whether I restart the phone before reinstall or not. 

I forgot to mention that it doesn't have an entry on iCloud in the settings app.
Being an app developer myself, I know that it is possible to store data on the cloud, or in the phone's keychain. Either way, the data is not deleted even if you delete it and reinstall it. Deleting the app makes the data inaccessible, however it is still there. Reinstalling it just makes it accessible to the user once again. Hope this helped:)