How does Quettra Portrait get the list of installed apps on non-jailbroken iOS devices?

According to the Quettra Portrait for iOS Privacy Policy they manage to get a list of installed apps on iOS. What's more, they're able to do this from an App Store approved app on non-jailbroken devices. Every Google/StackOverflow search I've done on the matter suggests that this is impossible, but Quettra is somehow able to do it without raising the ire of Apple. Any ideas?