Peter, I've looked at a lot of census's and have run across this before. It's almost certainly the same fellow. You can speculate on why, but perhaps he lived with his parents part of the time and at the farm part of the time. On census day he was "betwixt and between". So they both registered him. He probably only slept in one of the places that night, but each wanted to make sure he was counted. That's my guess on why.