There are probably many other examples of expressions whose generally understood meaning does not strictly correspond to the words used in the expression, and I've been sitting here trying to think of some but can't. Sorry, some other examples might have helped to clarify things.
That's just anything idiomatic, by definition, eh?
"I don't have a dog in this hunt"
"He killed it!"
"My team died in the second half"
"I'm dog-tired"
and so on.
Technical phrases, when used in common speech, tend to become idiomatic usage. Idiomatic usage tends to drift over time. A technical phrase, therefore, may easily enter the vernacular with a meaning close to or identical with the technical one, but that vernacular usage will tend to drift over time.