I think the same thing. Regardless of the intent, hoax or not. This guy did indeed gut out a G5 and put a PC motherboard inside. The way he described it make me believe he really is clueless. Even to pull a prank like this, I doubt anyone with even moderate experience would want to gut out a G5 and hope to put it all back together in one piece. I'm willing to bet that he did this intentionally and it's still that way right now. He just countered back and said it was a hoax because so many people yelled at him.
Image someone coming to his house and knocking on the door, "Excuse me, but your son is a moron. Do you know what he did to that beautiful Apple G5 you gave him for X-mas?" I'd sit back and watch them beat the crap out of him and just laugh. But if he was getting all this attention, perhaps his parents would find out and he would get in a heap of trouble. That is why he is now calling this a hoax.
Coward.