He only knows that they live in Cheapside, that Mr. Gardiner is a merchant and that he is Mrs. Bennet and Mrs. Phillips' brother (and, as someone as said here, maybe Darcy assumes that Mr. Gardiner would be as silly and vulgar as his sisters).
Quote
Chapter 43
The introduction, however, was immediately made; and as she named their relationship to herself, she stole a sly look at him, to see how he bore it, and was not without the expectation of his decamping as fast as he could from such disgraceful companions. That he was surprised by the connexion was evident; he sustained it, however, with fortitude, and, so far from going away, turned back with them, and entered into conversation with Mr. Gardiner. Elizabeth could not but be pleased, could not but triumph. It was consoling that he should know she had some relations for whom there was no need to blush. She listened most attentively to all that passed between them, and gloried in every expression, every sentence of her uncle, which marked his intelligence, his taste, or his good manners.
The word "surprised" is emphasized in the novel.
