What's interesting about it is that it may show some evidence of synesthesia being education or culture dependent.
Using base10 for numbers is taught at an early age, when the brain is forming a huge number of associations for learning, but I don't think it's been shown that synesthesia arises purely from "nature" (genetic) origins. So with the right thoughts, anyone may be able to push themselves into this state.
Author coming up with a system, and the system arising naturally are not mutually exclusive as far as we know. After all, what is natural vs... vs what, really?
They are describing how their brain naturally sees numbers: which is commonly referred to as synesthesia.