Some time back, I heard from somewhere that Rough Draft Korea actually assisted Digital eMation in the overseas animation production for this, albeit uncredited. How it worked was that Rough Draft did much of the animation of the Simpsons characters, and Digital eMation did the animation of the "Family Guy" characters and settings, and they combined their animation with Rough Draft's in the coloring and compositing stages, since such digital technology can make it easy to do so. There are a few bits here and there where it looks like eMation animated a Simpsons character, most obvious when their movements are more jerky and limited like a "Family Guy" character. One fairly obvious bit is when Peter and Homer are walking up to the gas station; Homer's animated in a somewhat choppy "Family Guy"-esque style by eMation, and then when the shot changes to him and Peter drinking from the gas pumps, Homer's animation switches to Rough Draft and looks like how their usual Simpsons animation does (especially the Matt Selman episodes). But I guess since Rough Draft was only providing character animation for much of the Simpsons characters, they chose to not be credited. (Rough Draft also animated on some Season 2 episodes of "Family Guy", and they also worked on the animation of Brian and Stewie's television song number from the 2007 Emmys, so they were no stranger to the show.)