Become a MacRumors Supporter for $50/year with no ads, ability to filter front page stories, and private forums.
I wouldn't be surprised if they were using a private API the App Store reviewers missed and if this was shot down by Apple. I don't know of any other app allowing screen sharing on iOS. Well, I'n not going to pretend I know the millions of Apps on the App Store so I am happy to be enlightened. Any other examples out there?
Good question. I did a quick search and found:

Squad – A video calling app for iOS with screen sharing features (iThinkDifferent article)

Squad - be together (App Store)
 
Register on MacRumors! This sidebar will go away, and you'll see fewer ads.