You all three are right. Cover swipes are not mentioned in Tutorial. I also thought they were buttons when first saw them. The only place I learned about cover swipes was one casual comment on TJC.

I was tempted to say Apple would never introduce something as confusing as cover swipes but then, they introduced pinch to zoom, did they not? It is also not something I would think of first. When someone handed me an iPhone with a map on a street a few years ago, I looked for buttons to zoom in, until I gave up and asked.

I would prefer fully interactive covers myself. Not two swipes (or buttons), but as many as the developer deems fit. Like what we have on widgets on other platforms. That's what covers are, after all. Widgets in disguise.