The post describes turning down a lot of qualified people because they had not encountered any applicants of required race/gender yet. In fact, they ended up not hiring for the position at all because they never encountered applicants of the required race/gender. So despite the fact that they had qualified applicants, they ended up forced to hire nobody. No individual person was discriminated against, but the group of applicants sure was: none of them got hired, despite the fact that the manager had qualified applicants and wanted--needed--to hire one.

The post also notes that this was invisible to people who weren't a manager, so it was effectively a secret, whether or not it was intentionally so.

If I tell my recruiters to never interview black people, it's not discrimination because it's not actually prohibiting them from hiring or promotion? Quotas in choosing who to interview or who to consider for promotion is absolutely a form of discrimination.

I've worked at a company that implemented this. It resulted in a vast double standard: white and asian males only got interviews if they came from elite colleges or well-known companies. Diverse candidates could pretty much come from anywhere. This resulted in a substantial disparity of tech-screen pass rates. Which the company held up as evidence of discrimination, and demanded that we address this disparity. Proposals to anonymize tech-screen, strangely, were ignored. Instead, recruiters (who had bonuses attached to diverse hires) got to decide who advanced from the tech-screen to the on-site instead of engineers.