Did a bit of investigating. This is acutally sort-of intentional. Basically we are storing your credentials in the hardware encrypted OS keychain. This means when the app is reinstalled the OS finds these stored credentials and uses them to log you back in.

This is similar to how Google and other platforms work on iOS/Safari. And storing credentials in the keychain provides a level of protection we want our users to have (for example, fingerprint access requirement and potetnially sharing across Safari/iOS).

I think the issue here is that this happens silently and "just works" when the app is reinstalled. Rather than remove this functionality (and lose the advantages of Keychain storage), we should consider popping up an opt-in message "Wikipedia login information found in your keychain. Log in with stored username and password?" with options to login, ignore or delete the keychain entry.

Taking out of scope of 6.0 as there is a bit of complexity to any solution and scope on 6.0 is pretty full.

@JMinor Thanks for the investigation and explanation!