I think an important part you might’ve missed is that the tag has to be away from its owner to be considered stalking you. If two strangers ride a train together, their air tags won’t be considered stalking each other.
That is the test in the first two bullet points. If the AirTags don’t listen then you’d have to add a “I am responsible for that AirTag” broadcast message from the responsible device. But I kind of suspect they do listen, if only for a short period after a beacon message. They need to get their public keys from somewhere.