He's talking natural to the relative location...not a sneaky infection via blankets by a bunch of colonialist descendants who brought the damned disease with them in the first place.
Dude no one new about germ theory until the late 1800s, and it wasn't widely known for a while after that.
All "myths" are based on some truth. Read carefully and comprehensively https://web.stanford.edu/dept/HPS/MayorSmallpox.pdf
The first small pox deaths in the Western hemisphere occured among the Aztecs shortly after 1500. The word Germ didn't even exist.