They aren't organized by the Sate. They have no official authority. So they aren't really a Militia.
They are a literal gang.
Stop calling them Militia.
It's a term used to describe a military force comprised of civilians. There's even a modern connotation of being against the state.
a military force that engages in rebel or terrorist activities in opposition to a regular army.
Gangs aren't purely for military purposes, so if the purpose of this gang is an armed attack against a govenrment agency, then it's not unreasonable to call them a militia.
Boiled down, "militia" doesn't mean much more than "group of non-soldiers organised in a soldier sort of way with the intention of doing soldier sort of things".
I think the term is private vs state militias, and with this article being about armed militias, we are talking about armed private vs armed state militias. I think technically all 50 states have laws on the books that prohobit various forms of private armed militia activity. Is it enforceable? Maybe, but that would maybe probably cause a nation wide incident given the amount of violence these groups can wield (though they would probably still lose against any organized state militias or any official state/federal military force), as well as increase the chance of a homegrown insurgency popping up. That's just my armchair opinion or thought about it though, I'm just armchairing here.