Seemed to work really well specifically with city government jobs (New York), based on the response/application ratio. I'm guessing it may have to do with their antiquated systems.

That's plain old keyword stuffing.

never thought of for resume

These resumes however are all identical to one another. It's a different situation, but that notwithstanding— we still do review all these and your sentiment very much aligns with my own.

IMO, this technique has been exaggerated to the point of being counterproductive.

As soon as the interviewer discovers that some claimed experience on the resume was a lie, they can't trust the rest of the resume. The interviews get harder and the interviewer starts looking deeper for other inconsistencies or outright lies.

Often, discovering outright lies on someone's resume is sufficient to drop them out of the hiring pipeline completely.

Spamming keywords that you don't actually know might get you into flawed companies that don't know how to screen or interview candidates, but those generally aren't good places to work.

The main thing I was talking about is using something like tiny white color text to reiterate stuff from their post. Or literally say I don't have any experience with X, Y, and Z. It's not lying, a printout doesn't show it, but it can trick the system.

One other example might be using the same inflated wording that job postings use (puffery?). Using fancy jazzed up language sometimes helps, especially if it includes keywords that are reasonably true or a matter of opinion (like the job posting saying it's a great opportunity or cutting edge tech).