In this example RMS made a request to the audience. A boundary would be something like "if you post photos of me to Facebook, you won't be invited to my conferences" or "if you do X, I won't interact with you". Might be difficult to enforce, but that's on the person making the boundary.
That's the defining feature of a boundary: you don't actually tell people what to do. You just tell them what you'll do. "Don't talk to me like that" is an ask, "Talk to me like that again and I'll leave" is a boundary.