Richsea,
We have no idea whatsoever how it happened. This was only our 4th cruise with Celebrity.
We did hear that there was a very large group from Germany that wanted to have cabins close together, and that was why it was done. So who knows. Probably the luck of the draw.
Needless to say, it was a suprise. We spent the first 2 days thinking that someone would tell us that it was an error and we would have to move. But that didn't happen, so we enjoyed it. We had no idea about what to have the butler do though.