Okay, let’s say he read medical journals. How many people can claim that they can map out a complex surgery which the biggest doctors, with years of schooling and experience, couldn’t do, by just reading medical journals?
Yekke2, the answer is zeh v’zeh gorem. Which is true whether or not he read medical journals, we would just say zeh v’zeh v’zeh gorem.
There are many gedolim about whom nobody claims such medical knowledge. What the Shevet Hakevi is telling us is that certain gedolim were able to draw upon their Torah knowledge to develop medical skills, but he doesn’t claim it about every gadol, even of the same or higher level.
So what makes the difference? It might be their specific mehalach halimud, it might be innate skills, and perhaps they read medical journals (we certainly know that the Chazon Ish didn’t go to medical school).
Whichever it is, or even if it’s all three, it doesn’t change the fact that they drew upon their Torah knowledge to develop incredible medical skills.