new info rercently published -air vs grain as source of wild yeast

I've just received a copy of a book on sourdough baking recently published in Australia.  The comment made in the first chapters of this publication is that 'feeding' sourdough starters is just a misnomer, and that when we add flour to our starters as a proposed food source, what we are in actual fact doing is "adding more yeast" (wild yeast). The author states that the wild yeast exists exclusively on the grain.  Interesting because I've never heard it put this way.  Any thoughts??  Are we just adding more yeast to our starters? If that's the case, what are the pre-existing yeast up to?? Just hanging around? I can appreciate what this new author is saying but it doesn't tell the whole story of 'culture'.  Given my prior & extensive knowledge/experience of sourdough processes "adding more yeast" just doesn't generate an image of someone who has a credible authority...  I'm interested to know other's opinion on this author.

Cheers