The party pack achievements?

Does anyone else have the achievements for the party pack on their list? My brother have them (at least two of them.... maybe that's all there will be). He checked his list the other day and instead of the usual 48/50 (he don't have a camera) it said 48/52. After looking at the two new ones it was clear that they are for the party pack. For some reason he have them, but I don't.  I can see them if I compare games with him though. The only thing he has done recently is moving all his files to a new HDD when he bought an Elite 360. He haven't even played the game since early June or something like that.