From the article:

> Or maybe—and this is the theory I like best, but can least substantiate—“No, totally” is really a contraction of “I know, totally.” That is linguistically improbable; I know of no instance in the English language where a homophonic slippage of this sort has taken place. But I like the theory anyway, because it captures what is often the semantic intent of “No, totally” with uncanny precision: I understand, and I am fully in accord.

When I say or read no, totally, I don't think "know" in my mind. I think above comments nailed it. It means "no question" or "no need to go on" to me.

As a counterexample, in spanish, we say "No, claro", and we don't have anything similar to "know".

saber/conocer?

Unless I'm missing something?

The crucial point is that "yo sé" couldn't be shortened to "no", in the same way that "I know" can be shortened to "no" (via "I know" -> "know" -> "no").