Anything you study for a few months you can become the world's leading expert on. It's a lesson I learned while doing my Ph. D. That's all it takes. After a few weeks, you get to the point where there are only a few others in the world that have read and are able to understand what you've read. A few months on, you are generating new ideas and insights. They might be wrong. But they won't be uninformed.

John Carmack did not start from zero. He already has a firm grasp on algorithms related to linear algebra. Basically machine learning is a whole bunch of matrix manipulation. He's been doing that for 3 decades. The rest is just absorbing concepts about how to apply linear algebra to ML. I'd say he's probably uniquely qualified to really absorb a lot of knowledge quickly on this. It's not about publishing papers, it's about reading and understanding the right papers. I have no doubt he can chew his way through lots of research material in a week or so.