the sight in the article is an iron sight, but not an "open" sight. It is an aperture sight, receiver sight or peep sight. See the definition of open sight here:
http://hunting.about.com/od/guns/g/definition-of-open-sights.htm The front sight in your article is a covered shaded "globe" sight. Also not an "open" sight. I shot competition for years. Not under NRA rules or NMLRA rules is that an open sight. for a sight to be open, the sight notch and front sight must be open to the sky. any sight where you look through a hole that is covered is not open. If you check the Williams sight catalog from a couple years ago, their offerings are separated into two divisions, (1) open sights and (2) aperture or peep sights. what is described in the article would be under the peep sights section. Under NMLRA rules, any shaded sight is expressly excluded from the term open sights, but is considered an iron sight, because there is no glass or mirror. Folks tried all kinds of things to cover the sights with shades that were open on one side but still kept sun light off the sight, those added contraptions became known as "Friendship cheaters". (Friendship, Indiana is the town where the NMLRA national matches are held)
For thirty years the PGC prohibited peep sights by requiring flintlocks to have "open sights" then with great fanfare about 2005, the PGC amended the regulation to take out the language requiring open sights, announcing that peep sights would now be permitted. and just 4 or 5 years later, for some inexplicable reason, they put the language requiring open sights back into the regulation. The digest still says peep sights are permitted, but the regulation does not. When questioned about this, somebody at the PGC said peep sights are open sights. If that was true why did they use the words open sights for thirty years to prohibit peep sights. I suspect that particular "somebody" has no idea what the term "open sight" means, had no idea about the history of the PGC's use of "open sights" and was covering an embarrassing mistake.
Just as an example, there are sights called X-tubes. these look just like a scope, but have no glass. they have adjustable cross hairs, just no magnification. They are a form of "iron sight" but certainly not open to the sky, so not an open sight. The shaded Globe sight, in the article, is just a shortened form of x-tube and is definitely not an "open sight"