I tried to hunt down the statement but without success. If I didn't imagine it, then I'm fairly sure it was in the Apple dev forums. However, I did find a posting where someone said they hadn't found the Swift runtime libs bundled with the WWDC app.

So, either the WWDC app had the Swift runtime statically compiled into the app, or it was written in ObjC. Checking the size of binary of the app should give a hint - the runtime libs you need to bundle are huge.