I knew from the start, but I would've figured it as much -- why else would they try to go through so much trouble just to seal a giant, scaly, hideous (whale) beast thingy?
It's pretty funny, My sister and I where playing the game and got to the imprisoned and we were guessing the imprisoned was Ghirahim's Master, or his pet XD... That was funny that he actually was his Master though, hehe...