The linked site explains the situation well. But the site is more of a commercial site than a news site. So I thought it best to put this post in Chat instead of News.
It is judicially created and so subject to various constraints. I am not saying right or wrong here, but this case says nothing about whether you can sue the federal official in STATE court for shooting you as a private tort, just as I can usually sure you in STATE Court for shooting me.
There are sometimes advantages to a plaintiff being in Federal Court (less likelihood of small town prejudice, maybe can get attorney fees sometimes), but this case does not have any impact on what state law says you can do to sue a person, federal official or not.