Do Facebook friends know when you post to a public group or only if they go to that group?

Will anyone actually answer this? Garbage community if not.

Been shadow banned, ever? ROFL. It's like in elementary school when you and two others girls whisper about a hated girl - you holding your hands up to your mouths while staring at her together,! You don't ever let anyone speak to that girl. You might make her kill herself! That's social media but the oligarchs who actually run it exist and your target really didn't stink.

My public group posts are seen in my FB feed by everyone, not just my friends. It's annoying to some outsiders to see shop talk of no interest to them, and it annoys me that my shop talk isn't private. I don't know why there's even a Public category for groups; it seems contradictory to the purpose of groups.