Fiber type doesn't necessarily dictate a muscles function. Muscle fibers are extremely plastic and more neurologically/demand mediated.
http://ptjournal.apta.org/content/81/11/1810.full
"Regardless of the classification scheme used to group muscle fibers, there is overwhelming evidence that muscle fibers—and therefore motor units—not only change in size in response to demands, but they can also convert from one type to another.
2,
18,
19"
"High-intensity resistance training (eg, high-load–low-repetition training) results in changes in fiber type similar to those seen with endurance training, although muscle hypertrophy also plays an essential role in producing strength gains.
33"
In the spirit of Occams razor noted earlier, I believe it is more of an ATP supply and demand issue. Repeated sprints, for instance, are increasingly reliant on aerobic energy production, even a 200m sprint is ~50% aerobic. Anaerobic energy production is VERY limited in terms of duration, we are aerobic creatures.
So to summarize:
Training repeated efforts of say, swings, allows for the fibers to adapt to that stimulus and improve that. With many heavy swings you are looking at making fibers that have relatively high force production but also has oxidative capacity to support the effort for a prolonged duration.
In the pure bro-sense of "strength" vs "cardio" then the above adaptation would indeed to "Third Way," to my understanding of it. Similar to Joel Jamiesons HICT training (which I have thought sounds much like USST with a 32kg.
Also to add to a lengthy post, much of the strength gains (and very probably endurance gains) are mediated by the brain, not by the physiology of muscles.