In fact, when you land on the FVF article the page gets scrolled to the height of the navigation.. so there is navigation, for those that actually scroll to top.
Yes, it doesn't get in the way while reading. Even if you are in the middle of the text and scroll up, it wouldn't change the simple info it contains - a logo, a title and some social media buttons. Only the people who scroll to the top would eventually get to the website navigation. We'll see how the trend goes - will it disappear completely or it will remain hidden way on top only for the true seekers.
great experience for navigating long reads. medium has very similar navigation patterns; i believe they started the trend.