Off hand, browsing the source, it looks like a web app (index.html, CSS, JS). "With offline support" makes more sense in that context too, as you would expect a native iOS app to be mostly 'offline' anyway (sans perhaps streaming video).

I think this means it's a website designed for iOS and using the new HTML5 offline storage stuff for local operation.

That would be more up John Resig's alley as well.

That's pretty cool!