The best part of the fediverse is that anyone can run their own server. The downside of this is that anyone can easily create hordes of fake accounts, as I will now demonstrate.
Fighting fake accounts is hard and most implementations do not currently have an effective way of filtering out fake accounts. I’m sure that the developers will step in if this becomes a bigger problem. Until then, remember that votes are just a number.
I would think that they need to set a somewhat permissive threshold to avoid too many false positives due to people sharing a network. For example, a professor may share a reddit post in a class with 600 students with their laptops connected to the same WiFi. Or several people sharing an airport’s WiFi could be looking at /r/all and upvoting the top posts.
I think 8 accounts liking the same post every few days wouldn’t be enough to trigger an alarm. But maybe it is, I haven’t tried this.