This tweet is misleadingly worded. The solution was not posted on 4chan, but rather by an anonymous user on a “wiki mainly devoted to anime” as the original tweet quoted by this tweet makes clear.
The original tweet is somewhat confused though too because the linked wiki is an archive/summary of a thread on /sci/ which is one of the 4chan message boards. It's copied there because of the ephemeral nature of posts on the actual boards so you can't provide a permanent link, thus linking to the next best source seems the best choice.
That makes more sense, thanks for the clarification. The tweet saying that it was originally posted on a "wiki" and then linking to a wiki made me think that that wiki was the actual source.
change "wiki" to "message-board" and "mainly" to "originally" and it becomes accurate. It came from the /sci/ board on 4chan.
The follow-up to the other tweet says it was copied to that wiki from 4chan.