At least their saying "rootkit-like" in the article, unlike the title of the article, which says "rootkit". I don't believe a hidden directory would justify as a rootkit, it's just a little more than a hidden directory that can't be seen by the GUI. Honestly, I think calling this directory created by the software a rootkit would be calling the Windows hidden directory that handles the Windows updates a rootkit.
I'm not a fan of Sony, especially after their real rootkit they installed with some of their CDs but I think the article is a little too extravagant.