This article seems to be a legitimate source.
It terms the system that carried out the attack as "the Great Cannon" and then moves on to attribute "the Great Cannon" to the Chinese government in Section 4.
As "compelling" as it sounds, the "attribution" in Section 4 seems rather short and lacking technical details and proper references as compared to other sections (Also I would not consider references from GreatFire as legitimate). So I am not fully convinced about that section.
Anyway thanks for sharing this. I definitely picked up a lot from this article.