I would think he's basically saying like, everyone having certain affinities for certain factors of performance, and a certain degree to which they can 'retool' or 'specialize' their factors of potential to a certain area of performance.
So you know, the old 'having a given level of potential and training bringing improvement are both true', in so many words.
On the subject on the OP, i think it can be helpful to break it down first into basic principles. A simplified explanation of the dynamics underlying the effects of that set of behaviors sometimes called exercise is the stress-adaptation cycle; placing the body under a certain stress it can recover from (key qualifier), and it adapting in order to ameliorate that sort of stress in the future.
So then. If one's goal is to throw a punch harder, then it brings up the obvious consequent: how do you add
increased resistance to the punching movement? Or more broadly, movements that
participate in the punching movement?
People have given various answers of varying felicity over the years, such as wrist weights, or stretch bands, or so on. In my view though, the safest and most effective ways of adding
significant amounts of resistance to a punching movement, would be, primarily, through sled drags or prowler pushing, and secondarily, through club/macebell swings.
I would say drags more than prowlers though, since most prowlers are fairly low to the ground and to push it you would need to hunch over like you're in a rugby scrum, while a sled can be used more sport specifically, with a rope or stirrup one handed using the same stance and form you would use in a fight, which is the most important thing you would want to add resistance too.
Exact implementation can take various forms to suit your needs, from high loads at any speed for building up maximal, to lower loads for 'sprint' bursts at high intensity at intervals, to long(er) duration works for muscular endurance. A fight itself can often demand a fighter shift rapidly between different levels of effort as dictated by his gameplan or the vagaries of the dance with his counterpart in general (which is one reason why i think the 400 meter dash is a great exercise [through perhaps not implemented through constantly running counterclockwise]; hits all three energy systems, in particular making you burn through the first two and hit 'the wall' before you can fully complete it [
https://experiencelife.com/article/all-about-your-metabolic-energy-systems/ ]).