That means Apple has declared the app non grata and pulled it. That's part of how the App Store system works. If an app is found to be a scam, or dangerous, it can be deleted by Apple not just from the App Store, but from every device it's installed to. In other words, Apple did just what people have been asking for here - do something about it. Well, they did. They kicked the app, and probably also the developer off of the App Store.
If the author had removed it from the App Store, it would remain on your device. But if you later deleted it, you wouldn't be able to download it again.