That's because it basically is. It doesn't have a traversing turret. Personally, I've never seen a shortbarrel version before, but I haven't researched them much.
The modified drive sprocket, gunner's sight position and spoked idler wheel make this an Ausf B. Early StuG III models employed the short-barrel, lower velocity cannon as their intended role was infantry support (as with the PzKpfw IV early versions). Up-gunned models were introduced with the Ausf F in 1942, as enemy armor became a greater threat.
Half of the posts here are of, in fact, the orignal KwK 37 L/24 versions.