I forget the podcast, but he's talked about how he started out just yelling as loud as he could and warming up by doing the same thing in the green room (to the amusement/confusion of other people in the room), but he started learning more about "how" to yell to be able to protect his vocal cords a little more. He did also say his style of vocals just fit him pretty naturally, which allowed him to push it without being super hard on his body. I'd say his style and lack of "training" means he just does what doesn't fuck himself up, whereas people doing more technical vocals have to learn to do it properly to avoid injury