I thought it was an Oceans 11 reference. Or more specifically, Oceans 13.
Hated the Hobbit. One and only book I got halfway through and just GAVE UP on.
Maybe you could look into the animated version of it: I used to watch that over and over when I was a kid. From the perspective of someone who knows the original story the animated version is super-abridged, cutting out all sorts of important stuff, but it did tell the story in a way I found interesting, and it served its purpose in drawing my attention to the original. Tolkien's writing is dense: there's no question about that, and it can definitely be hard to get through, but it was also absolutely foundational for Fantasy as a modern genre.Any
way, the simple explanation of the joke is that the original group of people for the adventure numbered 13, and the protagonist (who they hired to be their party's "burglar") was number 14: the lucky number.