I thought this at first, but if you look at a bracket like the one in the article on Amazon[1], it seems that they are mounted correctly, since amazon describes its depth as 19.5", and a height of 13".
Those brackets are different than what I would call standard shelving brackets[2], which should be mounted with the long side against the wall.
I've never seen a bracket meant to be intentionally mounted long-side-out, but I agree they seem to be advocating it there. You could do it if the loads were light, of course, but with a deep shelf and/or heavy loads it creates a lot of pull-out stress on the screws near the 90-degree bend.