They are not clever enough to have just used the word capacity without explanation and expect the audience to catch that they are not talking about capabilities but capacity. The myth came from:
"In the 1970's, psychologist and educator
Georgi Lozanov, proposed the teaching method of
suggestopedia believing
that we might be using only five to ten percent of our mental capacity."
http://en.wikipedia.org/wiki/Ten_percent_of_brain_myth
Which has been debunked. There is no need for us to think that the scriptwriters were going with anything smart here. It doesn't look smart, and we don't need to defend them either. It looks like an excuse for a super powered hot girl to be beating up people and shooting bad guys. Generic, uninspired looking, predictable already. The only thing we don't know from what we saw is if she dies at the end or not.
We both know they are using the word "capacity" to supplement his speech. We all know that they are referring to the "we only use 10% of our brain" myth, and they just used the word capacity which most people don't, that is all.
We use about 70-80% of the brain's "capacity" in particular, and use use all 100% or nearly all 100% of the parts of our brains on a daily basis. Either way that they might have chosen to word it, we know they are talking about the 10% myth. There is no untapped parts of the brain or any of that. Just people who have applied themselves harder and have more intelligence and focus and can think faster, better, etc. But no hidden brain capabilities and things like that. There are some exceptional people, but the brain of Richard Dawkins does not funking any differently than your brain or mine or the brain of any other rational, healthy, fully functioning human being.
