This is the Apple customer feedback for the Twitter iOS app. The app itself is wretched, which is why I joined many others and switched to the admirable Tweetbot.
So does 2.5 stars out of 5 mean the app is rated well by half the customers and badly by the other half?
Not at all. The lowest possible rating for apps is one star, not zero stars, so the average score is not 2.5 out of 5, but 1.5 out of 4.
There’s a trick to see through the deception though. If you cover up the left hand star in the red average rating then the truth will be revealed.