Earlier quoted context omitted.
Most popular websites gather a lot of intelligent people. Nothing specific to 4chan.
4chan was very early, if not close to first of what we'd describe as a "forum" and persisted through the decades. That's the notable factor, outside of all the "noise" described above. But yes, the noise was also a part of the surprise factor here. Many people have this perception that intelligent people are dignified, studious,and fancy in their demeanor. So someone like that hanging out on an "anime forum" can be s…
That feels untrue. 4chan was launched only in 2003. Forums are much older than that.
Especially if you count forum-like things that aren't called forums, like usenet or bbs.