This appears to be a weekly chess column in the newspaper, and they all seem to have a chess puzzle in them[1]. I suspect in the paper it would be at the end of the column, with the answer on another page. It's perhaps a bit of an inelegant way to present it on the web version, but that's probably some sort of tradeoff with how the Guardian's website works, and if it's worth adding some sort of special case presentation for the chess column, which probably isn't exactly the most read bit of the site.
