Think of some politicians claiming they stand for "freedom". Freedom from what and freedom for whom. My freedom to do anything I want, carry a machine gun for instance, interferes from the freedom others want to be free of gun violence. So when talking about freedom we have to always consider freedom for whom to do what? Similarly "free will" must be qualified by: free of what?
I think a good answer is "free from coercion by others". Now, you can coerce me to do anything, to say anything, and really to WANT anything you want me to want, by threatening my life with a gun. So, we only have free will in as far nobody is infringing on our basic freedoms.
And in this case, is the issue weakness of will, or is the will determined to do what seems best based on its available knowledge?
This has to do with the point about agency in the article. Everything in your "light-cone" can and will affect what decisions you make. But there are so many butterflies in your light-cone that you cannot say any one of them (alone) decides what your decision is. They cannot force your decisions and thus you have free will. No other actor can control your decisions. You are free of their will, thus your will is free of their will. Thus you have "free will".