I don't know, but I get followers like that every day. Given they tend to be people who are not Medium members, I suspect some of them assume Medium has a follow-back ethos like other platforms. I remember when I first got started on Medium, certain so-called platform experts who sold "webinars" about how to succeed on Medium recommended following lots of people and then unfollowing them after a while, to up follower count.

On the other hand, plenty of people read stories without engaging in any way. Many more people read my stories then clap or highlight or whatever else. So I can't presume a follower who never engages does not actually read.