I could have viewed this page maximized and just about read the whole thing without scrolling at all, but how would that be preferable?
You might fit more text on the screen but you don't read the whole thing in parallel, you slowly read paragraph after paragraph and what you gain in not having to scroll you loose in having to move your eyes and head instead, running maximized you just waste screen real estate.
I would have expected for this implementation to break down with different browser sizes but it reflowed well and seems to be well thought out. But I'm very skeptical towards such a radical change unless there is a real benefit to it. The benefit in this case is that you get reasonably sized columns (that are easy to read), which is kind of hard to achieve with vertical scrolling (I haven't seen a single implementation that works nearly as well as this one).
So I applaud their efforts, but there should be a manual fallback (couldn't find one), because I'm confident that it doesn't work as intended everywhere.