That and some of the active users are also bots. Lemmit.online is a good example; that community is set up to harvest content from Reddit via RSS and then Bots post it into the community. Other users (including bots) can then cross post it to other parts of the Threadiverse. “Lemmit.Online Bot” has made 20.1k posts in 7 days.

I wouldn’t be surprised if there are also hyperactive comment bots out there too.