I think the issue was closer to one where the interviewer (all but) hires the "non-diverse" candidate and then as an afterthought interviews the "diverse" candidate. This clearly defeats the spirit of the plan.

As for your specific hypothetical, it still seems to be contrary to the stated goals. My guess is you'd want to cast your net wide to get a cross-section of qualified candidates and maybe not just hire from the same sources that produce homogenous candidates