Sounds like someone took the base of Sludge & crossed it with some death metal imo.
To me that isn't sludge sorry man. The most heavy sludge band I know of is Iron Monkey Meth Drinker.
I love Iron Monkey and yeah, they are Sludge in a more pure form.
However, I'm assuming you've heard of Encycloedpia Metallum: The Metal Archives?
I would personally consider them the best authority on metal on the internet, and while I do not ALWAYS agree with them, they consider Primitive Man "Sludge/Doom Metal/Noise."
They are certainly some kind of MIX yes, and not the pure form of sludge that Iron Monkey, EyehateGod or Buzzoven are.
I am not sure all styles are always SET IN STONE.
I've seen your posts and you seem like a fellow "black belt in metal" to me hahaha.
Not to tute my own horn, but I've been listening to and researching metal and collected records and CDs for 25 years so I'd also consider myself pretty knowledgable.
You seem to know a lot more about and listen to a lot more black metal than me, while LATELY I am very into bands that mix all the extreme styles, especially blackened grindcore and blackened sludge, but if a band can somehow mix elements of black, death, grind, crust punk, and sludge that's the best, and I've heard several bands do it so far, not to mention some even including elements of meldodic death metal, industrial, noise and power violence.
I go through different phases and have been into most styles, but these days it's bands like Anaal Nathrakh, Fukpig, Dragged Into Sunlight, Sloth Herder, Lord Mantis, Watchmaker, Dephosphorus, Dendritic Arbor, Brain Famine, Bastard Feast, Sunlight's Bane, and many others that mix a bunch of extreme styles that catch my ear.
Hears an example of a band I've been digging lately: Sunlight's Bane.
Surprisingly they aren't on Encyclopedia Metallum right now and I'm not quite sure what I'd call them. They sort of fit a bit in with the new "blackened sludge" style but the sludge is really not very noticeable in that same way....so I don't know, you be the judge, I just know I like them: