They say that because the listener is so focused on exactly what is said, likely adding non-relevant context or missing context, and dragging out things instead of understanding the message that is being conveyed.

For example, when I say pick up trash to mean things to throw away and the kiddo focuses on whether she considers something that should be thrown away to be trash she is focused on what I am saying but not what I am telling her. "It isn't trash, I just don't need it." Then just throw it away!