An "academically correct" solution (i.e., not to taint the prestige of a scholar who cites the solution) would be to cite a real, proxy scholar who checks the solution, but gives all credit to the anonymous 4chan user. Scientists often abhor citing from blogs, forums, and Wikipedia, as those publications "are not peer-reviewed by trustworthy professionals".
I actually feel that the response here is a great one: "I feel like you should be able (forced even!) to cite things that aren't journal articles- even blog posts- if they contributed to your body of work. But citing things that aren't prestigious reduces the perceived prestige of your own, which is a perverse incentive not to cite." EDIT: I can't seem to figure out how to link to specific tweets, so this is the guy…
Here's the tweet you referenced: https://twitter.com/_delta_zero/status/1054820799473836032