But yesterday, I came across the reference again in suspicions that the Gurren Gakuen-hen manga got discontinued due to it ending so quickly. "Discontinued. It's like Swordmaster Yamato (Gag Manga Biyori)."
So then I finally went to research it. Sure enough, it's an episode from Gag Manga Biyori. According to Wikipedia:
In the first part, a mangaka phones his editor to complain about the outrageous and insane typos that appeared on his manga, Swordmaster Yamato. In the second part, a new editor, Takara-san, phones the mangaka to tell him that his manga has to end abruptly because of its low popularity, despite the story becoming intense. The mangaka is allowed three pages to end it - which, for a manga becoming intense, is absolute madness to the mangaka.
The episode itself.
Now it finally all makes sense. XD I also found two fan-made Gurren Lagann versions of it.
Enkimaster Viral (Typos)
Enkimaster Viral (End)