Anyone who was part of the HN/YCombinator scene at the time PG wrote that piece (and many years later) would know what the title alludes to. Why would it ruin this article's credibility?
Because when you quote someone, you should credit them. It's not believable that they don't know the source of the quote because it's trivial to find.
It would be one thing if the post was arguing for or against the substance of that essay, but it's really not -- it's about a different thing you can do, in a different context.