It seems that the folks at Think Services, which is the company that produces GDC, posted up an early version of the slideshow that accompanied his talk at the conference this year. According to the image accompanying the story, this early version references a product simply called "Lego" on one of the slides and makes references to an unannounced game in other spots. This is a pointer to the rumored Lego Rock Band game that, according to said rumors, is under development with Traveller's Tales and is scheduled for release later this year.
The PDF linked in Teasdale's blog appears to have been updated, with the offending slide updated to remove the reference to Lego. If I may jump to conclusions, this probably means that, at one point, MTV Games had planned to announce the game at GDC, but, after this initial PDF of slides was produced, decided to hold it off. Assuming that the image with Lego mentioned is genuine, of course.