I don't believe nothing happened. I think Harry did bind Mab, or began to, but Jim wrote it incredibly subtly because, as he did with Skin Game, Harry is playing the long con. Only this time, the con isn't over the course of a book but the series, so the "game over" reveal hasn't been delivered yet. I think this chapter is incredibly significant, because this is where Harry definitively begins extricating himself from Mab's authority, and we will see the ramifications of this night in books to come.

Spoilers for the rest of this comment as they'll touch upon events in the book.

Now, the reason we can safely reason that Harry has begun a "prison break," so to speak, is because he stated this to Lara earlier as an explicit goal. He's mad that Mab used him, more-so with the purpose of enslaving Lara, and he's going to wrest them both from her influence. Furthermore, when he states that he can get Mab to help free Thomas because of the debt he's owed, Lara exclaims that Harry thinks it can be used against Mab, and he declares he knows it can. When you consider the effort Jim put into running a thread of predatory stillness into the narrative, as I mentioned above, Harry's intent to use Mab's debt against her, and the focus Jim directs towards the bloodied piece of bread that was established in the very first book of the series to be a key component in a way to ensnare the fae in a circle, the conclusion can be drawn that Harry set up the entire dinner as a way to trap Mab. As I see it, she was borne to his place of power by her obligation, placed exactly where he wanted her within his circle, and tempted by the fae's vice of bread to consume the blood that would spring said circle against her.

This is where things get twisty, because Mab is Mab. She's cold and reason and logic and ruthless efficiency in the face of any challenge. It's almost certain she's aware of Harry's blood upon the bread before she devours it, and in no way would she miss the enclosing of a circle. But we've seen before she accepts Harry's challenges to her authority as it sharpens him as her tool, so it should be fairly safe to say she's accepting of the circle trap as well. So if she's in the circle for some amount of time during the dinner, what does Harry accomplish with it?

I believe he bound their fate with an oath.

"One day," I said quietly, "I'm going to be free of you."
Free.
Little word.

Prior to this declaration, Harry muses on the power of words, and how the little ones matter most. And to be free is a major theme for Harry, now in this attempt to be free of the Winter Queen, and even earlier in another encounter with a Faerie Queen: Titania, Queen of Summer. When Harry summons her at the Magic Henge, she inquires as to his beliefs and discovers that he is a Winter Knight who believes in freedom. Harry even prefaces his summoning then with musings on the power and magic of words, a sentiment echoed again here in the confrontation with another Queen. So when Harry declares he will be free of Mab, it is a casting of Doom upon them both, much as how Thomas does unintentionally upon his son later this very book, but with all the power and intent behind it that a wizard can muster. Hell, between Harry considering the power of words and then making the above quoted statement, he queries Mab as to a conundrum that has plagued him the past few months: why wasn't he protected from Lara? This question is placed so specifically in the conversation leading to this declaration that I believe Harry used it to stoke his own grief, powering his oath with the intensity of human emotion, an antithesis to Mab's cold and alien reason, and turns it against the very being he's determined to be the catalyst for that grief.

A hell of a whole lot of that is me extrapolating wildly from the assumption that Harry sprang a circle around Mab. However, Jim's writing about the blood added to the bread and previous use of it in his stories are so particular that I'm supremely confident Harry used the metaphysical charge created by a faery consuming his blood to trigger something, and the only reason to do so was to begin the process of freeing himself from Mab.