Bluesky doesn’t show your posts to any accounts you’ve blocked, at least on the main client. 

It’s so open that, yes, for now the blocks are public but they’re working on private states, so that things like private accounts & posts can exist. I’m guessing they’ll migrate your blocks list to that whenever it comes, but it won’t be too soon.

And you can enable a feature which hides your posts from anyone not logged into the official Bluesky clients. 

Obviously because all the data is public anyone can fetch it from the API and look at, well, anything really..