>I'm wondering if someone I follow engages with the content I can see it?
Yes, very likely. "reject" action triggers when a remote server sends messages to you. But when someone is interacting with a post, your server pulls it from a remote server.
>I don't want them to see my content
This is also not supported.
I plan to address these shortcomings, though. Meanwhile, you can block incoming and outgoing requests to certain hosts at the OS level.