The Guard is not referred to as an SE in that article.The Guard is actually classified as a pivoting head SE.
Also the article states:
"The Leaf razor is probably the closest thing to a cartridge razor in this article–"
And then writes about the Guard which is a single blade cartridge razor and the article admits as much:
"Gillette uses the cartridge in their new Treo razor,"
"The Guard uses a proprietary cartridge with a single blade."