Totally. He probably sees the difficult child do all sorts of nasty spiteful things to the other kids and get away with it! Who knows what this kid does when the teachers aren't looking and the other kids dont tell on him, but just put up with it and give him his own way!
It's horrible when your little angels start changing when they go to school. That's one thing i noticed with my DS.
You just have to make sure, i suppose, that he knows his behaviour will not be tolerated at all because if he gets away with it, even just slightly, he'll continue to act like the difficult child at nursery.