I agree with jeffrey and Lenora that the author is deliberately planting these little tidbits - but JanetR makes a very interesting point above - consider the source of this information! We already have some decided opinions of Miss Bingley, and may not be inclined to believe what she says about Mr. Darcy, since our evidence so far is to the contrary of her testimonial. Thanks for pointing out this little bit of gossip - Miss Bingley and Miss Bennet talking about Mr. Darcy. It bears remembering as we move forward in the unfolding of the story.

Also, I would second what Adrian says below - that the picture we have of Darcy becomes more complete in Chapters 7-11 where we see more of him interacting "among his intimate acquaintance. With them he is remarkably agreeable." I agree that Darcy seems at this later point in the novel to be an agreeable companion, engaging in conversation. I don't think it is too much of a stretch to believe that the conversations reported in the text are the only ones that occur - over the several days there would have been more opportunity at meals, etc., for all of the party to converse, and for additional information about the characters to be revealed to their companions (well, perhaps not Mr. Hurst!).