Gregory's ServerAll of this speaks to the issue of decentralization, btw. Ostensibly, Bluesky is built for federation between multiple PDS, the protocol's version of instances. AFAICT, though, PDS only communicate with one another when you @ a specific user on another server. Most of the time, they're just middlemen between your client and the indexing servers. The indexing servers are making most of the real decisions about what shows up in your timeline.
Bluesky is centralized around indexers.
In theory, there can be multiple indexers, and you (or, at least, your PDS) would be able to choose between them. In practice, though, it's going to be incredibly costly to run an indexer, so expect corporations and VC-backed orgs to dominate. Bluesky has the first-to-market advantage, so they'll be the big one. Twitter could well pivot to indexing on the BS protocol. Maybe a few others will pop up. That's what decentralization really means here: Your choice of corporate-run indexers.