The author (human or llm) flips between performance ("millions of vectors") and semantic accuracy ("only 3 match your filter") to push its point, depending on what needs to look worse. AI framing switch that was that was probably introduced by RLHF on humans that don't think critically but want somewhat convincing answers.

For pre-filtering "You’re still searching millions of vectors" isn't valid argument, because the author does not relate to any alternative, and post-filtering is even worse.

Author is a human :). Performance and semantic accuracy are both important. The point about pre-filtering _youre still searching millions of vectors_ is important because once you apply a filter you can no longer use your vector index. And doing a full scan on millions of vectors is quite expensive