In Japan, it's not uncommon for books and manga to be promoted with Japanese internet forums, such as 2chan. Retailers and publishers might put stickers or banners that say something is popular online. But, as website World Three pointed out, they've expanded.
At the bottom of Japanese manga It's Not My Fault I Don't Have Many Friends, there's a string of text that reads: "海外の2ちゃん的な掲示板で大人気!!" or, loosely, "A smash hit on the overseas version of 2chan!!"
The overseas version of 2chan is 4chan. Since more people in Japan are familiar with 2chan, the publisher chose to package the 4chan as the foreigner version of 2chan. It's just easier to convey.
The manga is already a sleeper hit on 4chan, where it's getting an English language fan translation. The reason why this manga in particular seems to have touch as nerve is, as tipsters Reinhard pointed out, "because the protagonist is similar to the social awkwardness and fears many users of 4chan go through."
That's Pretty Cool [World-Three — Thanks Reinhard!]