[keskival]

It's not illegal to omit citing existing work, like it isn't illegal to lie. It is highly unethical to knowingly claim to propose a novel approach which has been publicly proposed, and even implemented before though.

In effect this is erasing independent practitioners as inventors of methods from the history of science, and claiming false credit.

[bastawhiz]

So a reasonable remedy in this case would have been to strike the text that says the work is novel? When you say "claiming false credit" I'm assuming you mean "getting to claim credit for it being a novel idea even after being told it's not".

When I think of citations, I think of ways of references that also attribute credit. Maybe this is different in academia? At least for me, I'd see a citation in this specific case as improper, because (assuming they didn't know able the author's work) the paper doesn't include anything from the author of the post. It would seem to me that before you'd include a citation, you'd want to take the time to fully review the other work to see that it is indeed the same idea and also not a load of crock. Depending on the subject, that might be a substantial time investment.