i guess these are posts from the closed beta at https://staging.bsky.app/ which has maybe ~10k users now (they said >4k a while ago, and then apparently they invited 5k from their waiting list yesterday).
permalinks to posts there are currently not accessible without logging in, but i guess since this site exists there must be some API from which posts can be accessed without a login.
data is delivered over a websocket connection
const socket = new WebSocket('wss://bsky.social/xrpc/com.atproto.sync.subscribeRepos')