I think that came from one of the interviews over the last year about the comics, where Whedon basically admitted that Dawn's college boyfriend being something called a "thricewise" was something he hadn't fully sketched out what it meant -- but he threw it in so it could be "filled in" later.

(Incidentally, with Dawn's newest transformation into a centaur, there's renewed speculation that Joss is going to have Xander and Dawn "hook up" somehow. At the very least, Georges Jeanty, the regular artist for the series, told a fan at a recent con that Xander would "hook up" later in the season with a character "we've seen before," so that his recently killed almost-girlfriend wouldn't be the last nail in his lovelife's coffin. Can you say "ick"? If nothing else, I'm convinced that Joss is making Dawn, with her magical transformations, the Official Buttmonkey of the comics.)