I agree, some of the things Elizabeth says Mr. Darcy thinks she probably doesn't mean. We've been introduced to Darcy's POV that he's become attracted to Elizabeth Bennet. But I don't think Elizabeth has suspected that Darcy is actually attracted or interested in her. So those differing motives attributed to Mr. Darcy make something Elizabeth says sound to Darcy like willful misunderstanding, but to Elizabeth, they are merely the truth of what she thinks Darcy is thinking or meaning, but said in a humorous, teasing way.