There seems to be a bug in the SE app for iOS. Yesterday I've asked a question on Android Enthusiasts forum but I've found the answer myself. In the iOS app I see the same question listed twice as 'top post'.
Edit: @Patrick Hofman pointed out that this isn't a bug. However the app is lacking the icons to point out which top post is a question and which is an answer. I would like to propose his suggestion as feature request.