Believe me, when I found out how old the breed was, I was pretty astonished!
I was thinking about this, and I'm wondering if part of the reason that so many people believe in the misconception that Shibas and Akitas are related, is how Shibas were introduced to this country. Thinking back to some OLD early kennel advertising, I clearly remember a well-known Akita breeder advertising that in addition, they were now breeding "Shibas- the Little Akita!"
Early on, a lot of owners stuck trying to explain what exactly a Shiba Inu was to curious people, would get frustrated with the immediate jump to conclusions they would make. Apparently the name "Shiba Inu" sounded enough like "Shih Tzu," in their minds, that they would nod knowingly and say "ohhh, you mean those fluffy toy dogs!"
Obviously, Shibas are a far cry both in temperament AND conformation from Shih Tzus, and breeders wanted to make that as clear as possible- so of course, you couldn't help but slip into describing the "most similar" thing that your average Joe would be likely to recognize.
Despite my best efforts, I STILL occasionally find myself describing them as "sort of like a small, red (or black and tan) Akita," to people who have no clue what I'm talking about.