Bluesky feeds are a filter on the content. They look for particular keywords or exclude keywords, and if your note fits to that set, and you're allowed on the feed as a user, they add your post to the feed. This is the same way a topic relay can work, like https://christpill.nostr1.com
>>Feeds offer some of the same functionalities as hashtags, lists, or communities. A feed is simply a curated list of posts on Bluesky. The curation can be done fully openly, as with a feed that searches for any keywords and automatically indexes them. (This can approximate hashtag behavior and some feeds are keyed to hashtag-looking keywords, like #LandBack.) Feeds can also display all posts from some users or some posts from a pre-screened list of users.<<