Given the app consists of two web views and a bit of background code I'm not surprised. Perhaps if they'd utilised the GUI elements Apple provides to give a native experience it would actually warrant being an app.
tbh this seems like it would be better implemented as a HTML5 mobile site that utilises the new local storage APIs. You can still promote web apps through App Store, and it seems like a more obvious route to me.
Sorry, my bad. It seems I was thinking of PhoneGap, which packages HTML5 apps for mobile devices https://build.phonegap.com/
I believe on some Android platform (such as Amazon App Store) you can even charge for HTML5 apps, so it's not unprecedented.
However Apple app submissions requirements state you have to have sufficient functionality to warrant providing a native application. Not surprised that this code didn't make the grade, but as mentioned if they were able to make use of UI framework or put through PhoneGap could resolve the issue.
tbh this seems like it would be better implemented as a HTML5 mobile site that utilises the new local storage APIs. You can still promote web apps through App Store, and it seems like a more obvious route to me.