AFAIU, that's how lemmy federates content to mastodon.
If you didn't know, you can follow lemmy communities (and other groups) on mastodon, but the appear as users constantly "boosting" everything that happens in the community and so can quickly clog up your feed.
Mastodon now has exclusive lists though, which take everything that appears in the list out of your home feed, which is a nice way of managing it.
In fact, for a community I moderate, I've got a mastodon list just for that community, which gives me a reverse chronological feed of everything that happens in the community ... which is actually useful and not quite available from the interface (as you posts and comments have to be viewed separately, which isn't bad really).