I was under the impression that fonts are just a collection of line arc/points.
So is this a probabilistic comparison in that, if all of the line arc/points match another font - the chances are high it was ripped?
As a result, in one of the modes of PDF you can save the entire font file for every font used by the PDF into the PDF itself, just in case it's not present on the recipient's machine. Costly? Sure! But what else are you going to do if your document uses a super-special font for displaying mathematical symbols or sanskrit or the glyphs of a language understood by fifty people on the planet and Unicode isn't widely adopted yet, having been invented just two years before PDF?
So in this case, the author grabbed a copy of a PDF version of the ad (because those ads are still available online), cracked open the document itself, and found the glyphs for the letters are sourced from a version of the font that was intentionally created to steal someone else's font work because the whole font file is in the document.
Assuming it's for print/display and not future editing, I imagine you could convert the font strokes to vectors or similar.