Like, looking at what my hypothetical person 2 thought they were doing -- there is no need for them to assume that is a clean or perfect block, or that there is no way for it to get exposed. Most people who have used blocks in any sort of social platform know that with alt-accounts or friends, or just normal social dynamics, the person they block can find out. That capacity even with that limitation is nevertheless /enough/ for them to want it.
In this case, that still-CAN-be-revealed requires either active testing of each possible block, or very engaged social surveillance.
Which is often discussed, and which people seem to discuss and understand Bluesky's block issue as being qualitatively different than.